Not really a lot to do for the MTX75, you could go searching for some quaife gear sets, or for the same costs you could have a pile of spare transmissions.
3rd gear syncro can be weak, I had one fail, but I place most of the blame on the ebay shifter the previous owner installed in the car.
Parking Lot Hero
2008 WRX daily driver
2003 ZX3 23D Autox Car 42 FSP
"Hella Functional - Raced, Not Hard Parked"