Audible wow on Well Tempered TT

My 1987 WTT/TA has been trouble free all these years.  Lately, however, I've noticed some pitch instability...test tones are not absolutely constant.  The belt is a new one from LP Gear.  Anyone have any ideas on what can cause this and how to mitigate?
Pully, belt and platter need to be cleaned with a solvent like brake cleaning fluid. Oil the bearing. 30 Wt motor oil without detergent will do fine. 
Does the platter exhibit any run out? If you get down at eye level and view the platter surface on a 90° angle can you perceive the platter surface undulating? Those might be signs that the little plastic buttons inside the bearing well that support the platter spindle shaft in the lateral plane might be wearing, perhaps due to a lack of or insufficient lubrication over a period of many years. As you probably know, in the well tempered design the belt is part of the vertical bearing mechanism. It pulls the platter shaft in one direction while those two white plastic buttons stabilize it in the other direction at a 180° angle To the belt. If you remove the belt the platter flops over toward the unsupported side in the bearing well.
Funny coincidence it may be, since I just now been playing two records (at least) I can hear what sounds like speed instability too. 

On my Ortofon M20 (MI type) I changed the FL super stylus insert to the E super. This one has a VERY high compliance of 40cu, double that of the FL super. 
So what seems to happen now, that slightly out of centre LPs are 'pulling' the stylus back and forth while negotiating the outer grooves, clearly visible as it happens. 
The effect is a listening perception of speed instablity, a kind of 'groove wobble' induced wow! 

So definately no arm-damping for this type of high compliance stylus / cantilever insert - and next no anti-scate force setting - if any!
As it also will act as a form of damping on the tonearm's lateral free movement. 

The more restricted the movement will translate into unwanted horizontal cantilever deflections, and my best guess, sounding like wow, and more noticeable with slow drawn out music passages.
Examples are opening passages of 'Giselle' Act I and II. 
One more would be 'On the Beach' by Chris Rea.
Both my LPs have slighly out of centre holes. 
Michélle 🇿🇦 

Justmetoo, You wrote, "slightly out of centre LPs are 'pulling' the stylus back and forth while negotiating the outer grooves, clearly visible as it happens."  I don't know why or how the shape of the stylus tip would make that phenomenon more or less apparent or more or less a cause of wow.  Maybe you are saying that the increased compliance of the new stylus is making the phenomenon more easy to visualize, but you've quoted vertical compliance; that may have nothing to do with horizontal compliance. Off center LPs are an incurable cause of wow no matter what, unless you are one of the few who own the Nakamichi turntable that provided correction for this problem.  We often lament that no other manufacturer ever adopted this adjustment.  And the Nak is rare (maybe because it came out during the eclipse of vinyl reproduction by digital, was expensive, and did not sell well) as a result.
OF COURSE! and very much meant, the stylus IS attached to the cantilever!!! 😏 

AND OF COURSE still nicely tracking, following the record groove also! 

The stylus AND cantilever! VISIBLY moves about, deflects visibly, laterally, from the cartridge body, via it's suspension, no doubt. 

This cantilever/stylus deflection, pretty much is in consort of the wow heard - and given due to the described 'tonearm' damping via anti-scate force setting and/or silicone etc. damping trough (this given the high 40cu compliance) 

Please don't expect me to write a Phd theses on this now, please! 😊 

Not THAT hard to understand now, I think. 

If the compliance is a lot less (than 40cu, ~ <= 18cu) - 'visibly' - the tonearm, cartridge en complete, moves just fine with the off-center displacement, with no *visible* defection. 

I hope this will make it a bit more clear, if needs be? 🤔 
Michélle 🇿🇦 

Oh, and one more thing, you are seriously suggesting an e.g. 40cu compliance will only apply vertically ?!? 🤔

Looking/feeling the Ortofon M20 E super or FL super (stylus+cantilever) inserts does not convince me of that take, at all - as it is pretty 'wobbly' left to right, too to bottom... compared to the e.g. ORTOFON CADENZAS BLACK of less than half that Compliance ~ 18cu.
Michélle 🇿🇦 
I don’t know the WT decks from back then. What is the belt made of, I assume it’s not like the current WT decks’.
I had a similar problem with a Townshend Rock Mk2, which uses a round rubber belt, basically a 1/16” cross section O ring. After fitting a new belt there was speed instability noticeable on piano music. The belt was taking a set when it cooled after use. A belt direct from Townshend was the same so I ended up going back to a 10 year old belt. I’ve since replaced the Rock as my main deck but it still gets occasional use for mono, I remove the belt from the pulley when I stop it for longer than the time it takes to clamp another disc.