Should I get CAT SL-1 mkII updated to mkIII?

I just bought a SL-1 mkII preamp. The tubes are a couple of years old and I was going to retube it(almost $300 for NOS). Would I be better off putting that money toward the upgrade to mkIII($675). Any opinions?
Is it a line only or + phono? If the latter, I definitely preferred the MK3 phono. If only line, I'd think twice about the upgrade -- BUT, if you're prepared to pay $700 (and have the money readily available) you should go for it and think about retubing later.

Finally, if you can't get retubing out of your system just buy Svetlanas or Harmonix for now and worry about NOS later.

Good pre, BTW!
R U sure that is the price for upgrade to 3? I thought it was 1200. The 700 is for 1 to 2--1600 if you have a 1 to 3 at the same time.--Maybe they have changed the price---??
Gregm, It is the line only. Why do you say to think twice? Is the line only not that much better updated?

Avguygeorge, The price is $675 for my model of the MKII. Ken said that prices differ depending on the serial #. He said they made some improvements throughout time with the MKII. If my serial # was about 50 earlier it would have cost $875.
Pal: not that much better to these ears. Fact is, I don't exactly remember what was improved... I *think* upper end extension.
An update will also mean that the unit will be checked overall, so that's an extra bonus.
I definately prefered my MK II version. Wish I had NOT upgraded.
Hi, I also had my MK II update to the MK III and I also didn't hear $700 of upgrade.
Kawika, what did the upgrade do that you din't like?

From the comments so far it seems I may do better to just retube the MKII. Any suggestions on good tubes to use. I have read that CAT preamps will eat up certain brands.
Is an upgrade from the SL1 Reference Preamplifier to a later version available and, if so, at what cost? What exactly does it entail?