What's a real good arm for a Decca Cartridge?

I have a Decca London Super Gold with a paratrace stylus. It's sound as good as anything I've ever heard using my SME M2-12R arm on a rebuilt TD124. The problem is I want something that will track all my LPs and the SME just won't. After a bunch of tweaking, including adding tons of mass, it'll play 90% without issue. What arm will get me those extra 10%?
I run the same DSG/wP in a Jelco 850L with no tracking issues and sounds superb.
You might also look at the Groovemaster ll.
The Biotracer arm on the Sony DD TT. Servo-compensation for better groove tracing and elimination of arm resonance matching for different compliance cartridges. The Decca cartridge would certainly benefit from this, as it has much different stylus compliances in the vertical and horizontal planes!

Sorry for not remembering the model number of the Sony Biotracer TT! I do have one on hand in the other room! Pretty neat arm!
Terminator T3Pro by Trans-Fi Audio and you will never look back. Gets the best out of any cartridge. Enjoy the ride : )

@dhcod: Are you certain it is the arm not the cartridge that is responsible for the mistracking? The current London’s are better in that regard than were the Decca’s, but tracking remains the design’s major failing. The SME has long been considered to be a poor match for the cartridge; something about the huge amount of mechanical energy it puts into an arm causing the SME’s knife-edge bearings to "chatter" (that’s why adding mass helps).

Arms popular amongst the Decca/London cognoscenti include the Sumiko MDC-800 ("The Arm"), Zeta, Hadcock (and other unipivots), Mission Mechanic, Fidelity Research, Helius Omega, Well Tempered, linear trackers including the Eminent Technology, TransFi Terminator, and London’s own. Art Dudley even liked the London Gray in a Rega 300, but he’s not a Decca nut. There are some older Audiogon threads on the same subject.

If you really want to go all in, get yourself a Townshend Rock, THE table for the Decca/London!

+1 bdp24
There is nothing wrong with your arm. It is the cartridge, just one of the things you have to live with when you get a Decca. They can sound great but they do not track so hot. Just like any British sports car.  Most people I know with Deccas have other cartridges they can use on tougher disc. Instead of getting a new arm jest get another cartridge!

Poppycock! My Decca SG tracks perfectly in my 12" Jelco 850L at 1.65g. I have a Decca Grey Garrott Export in a 12" 750L and it too tracks perfectly at 1.7g.
I do use heavy mounting bolts (brass) on the headshell.

Touche', @noromance. What I should have said is that if you have a Decca (is the op's a Decca, or a London?) in an SME, and you have mistracking, I would suspect the cartridge before the arm. Not all Deccas mistrack, but they are well known to not be the best tracking pickups around. The best examples are fine, others not so much. I never managed to get a hold of a Garrotted-version; I tried to pry one out of Ken Kessler's hands, but he wouldn't budge ;-) .
The modern London cartridges made by John Wright have much better quality control than the original Decca Special Products output (which was indeed a bit of a lottery).
I have had Decca for 40 years now, and they will track most records. No they won't do the cannons on the Telarc 1812 Overture, but very few cartridges will track that.
Traditionally they were best mated to damped unipivots. The lack of vertical compliance meant that the vertical vector energy could be dissipated in the unipivot without affecting the cartridge performance. I've used my Maroon, Garrott Bros Gold and FFSS MkIV C4E (John Wright rebuilt with fine line tip) in my Hadcock 228 and Schroeder tonearms (Model 2 carbon and Reference) with great results.
Even the very best examples have trouble with the heaviest passages. Just get an Ortofon test disc and try out the vertical tracking band. I have done this with the London Reference and it could not do it. 
It is however a wonderful sounding cartridge and many people do not have that many albums that are that difficult. If you are a Metal fan and like Telarc's 1812 Overature you would be better off with a different cartridge. Decca cartridges are also notoriously unreliable. Perhaps there is a problem with dhcod's example but unless he hit the bearing assembly of the SME with a hammer it is unlikely to be the source of the problem. The SME can be set up for any mid to low compliance cartridge by adding enough mass hopefully using a test record to check the results. Oh, I happen to like Poppycock.
Thanks for all the info! I've got a test record on the way and I'll add even more mass to my Fidelity Research headshell. I've been lining the inside of the headshell with the lead tape that is normally used for golf and tennis equipment. That has allowed me to use the extra balancing weight of the M2-12R. I've been noticing since I posted originally that the mistracking happens almost always at the same place, about 2/3 into an LP. I wonder if I have to readdress my alignment?
If your alignment is *close* to correct it is likely not the culprit. How much does your 'dressed' headshell weigh now?
I would guess around 26g.

Here's a weird one. I swapped out the 3" maple shelf I had installed on my wall shelf just a month ago and went back to the 1/2" maple shelf I was using before and it has only misracked once since then in two days of listening. Either the rigidness of the thicker shelf was bad or somehow there was something wrong about how the table was sitting on the thicker shelf, even though I checked and rechecked the leveling. 
Hmm. Higher self resonance frequency for the thinner shelf? Interesting indeed.
A word about Trans-Fi linear tracker.
 All my higher quality cartridges, both very low compliant and very high compliant can do all the Telarc 1812 Overture cannons because the Trans-Fi  arm is capable. But only a couple of them can do the very last cannons with an authority that leaves me speechless. Trans-Fi T3Pro is able to distinguish true tracking ability with ease and obviously the true very finest cartridges. I don´t have a Decca Jubilee not to mention the Reference but my friend also runs a T3Pro and hasn´t had issues with his Jubilee. Trans-Fi linear tracker does the job.
While we are on the subject of Decca.

Does anybody know much about Decca London Blue, supposedly rebuilt by John Wright?

Sound to expect?
Might work out on the Nottingham table which has a fairly decent unipivot arm.

Or even on a Lenco......

Always been intrigued by them but no experience with them at all.

@uberwaltz, I can answer your question. But first, let me clarify the issue of the Decca and London names. John Wright had long been a Decca employee (head of the department that made their cartridges), and when he bought the rights to the cartridge name and design from Decca, he changed the name to London. The name "Decca London" can be accurately used only in reference to one of the cartridges made by Decca, the model named the London. Other than that one model, a cartridge is either a Decca, or a London. I see the two names conflated regularly.

The Decca Blue was introduced in the early-70’s, and was also referred to as the Decca Mk.V. It was a drastic redesign of the Mk.IV, and ushered in the new era of Deccas. It had a conical stylus, and tracked at 3-3.5g. It was my first Decca, bought new in ’72 (rhyme unintended ;-). I know, I know, the London website states the Blue was introduced in ’74. But I bought one in ’72 after: 1- reading a review of cartridge by JGH in Stereophile, and seeing and hearing one in the system Bill Johnson delivered and set up at Audio Arts in Livermore, CA that same year.

John Wright will rebuild, restore, update, etc. any and all Decca or London cartridges, including the Blue. Where did you read about a John Wright-rebuilt Blue? The Blue had been discontinued by the time John bought the company, so there is no such thing as London Blue, only a Decca. At least that is my understanding.

@bdp24 .

I am sure it is as you state with people just using the term Decca London and then tacking on the model name after, like Blue or Grey etc.

So if it is originally a Decca Blue it still has a good chance it was , as claimed, rebuilt by John Wright.

I read somewhere that after his rebuilds also depending on what stylus he used that vtf was reduced considerably to below 2g.

I am wondering just how much of the original Decca sound a rebuilt cart would still have?
SME 3012, or 3009 (series one) have both worked well with my Decca Red.

dhcod, not weird at all. With the heavy shelf your wall shelf was resonating at about the same frequency as the Decca/SME combination. Whenever the right frequency played the stylus was bouncing around in the groove.