I know that the best to use is the Synchromesh(spelled right??). But its hard to get it in here. I was at pepboys and found Mobil1 synthetic gear oil 75w-90 that can be used in manual trannys. Should I use it? Any other good alternative??

This is a for a NEW Isuzu MK7, not the MR3/MT3 originaly in the Fiero. This is a never done swap.

Thanx
DreX

As our normal recommended gearbox oil is 5w30, it looks like that may be too thick. That said I doubt you get the low temps in PR that we do here and it may be fine.

If it is a GL-4 specification, you can use it. The Ogre just posted a whole thing about this. You probably can find the info in his cave also.