Synchros seem to wear out a lot faster than bearings! My E51 only has 100Kms on it, the box is fine except its just a bastard to change gears fast at high revs in low gears (6K RPM upwards). Particularly 2nd to 3rd when done near 7K RPM is the show stopper.
All MR2SCs I driven have terrible 2-3 synchros. I think I'll just bite the bullet, whack in the E58, which will _hopefully_ work with my E51 selector.