It seems as if you are due for a tranny rebuilding or replacement.
In my 95, reverse was gone but all others shifted correctly. It ended up being that the oil pump cover, over which the reverse clutch assembly rides, was eaten up by the reverse clutch, causing a huge internal oil leak, causing the system to fail.
Funny thing, the replacement part I got from subaru, was full of sharp edges ready to eat the seals and the bushings in the new reverse clutch assy.
All the metal that came off the cover, ended up travelling in the hydraulic control system, etc. This could be the cause for the other gears not to work.
Good luck