348 gearbox weak points (if any?)

Just bought a 1993 348tb with unknown milage (yes, I know!) used for amateur racing for the last 10 years. Engine and gearbox appears fine at the moment.
There are numerous statements on the web saying that the 348 gearbox is not too good, but I cannot find anything specific.
Could anyone please answer the following:
What should I particularly look for?
Are there parts that would be sensible to change precautionary?
If I was to tune the engine, what Power and/or Torque Levels should I expect would be the gearbox limits?
Is this gearbox really not too good?