I remember reading that...

I don't answer too many MTX-75 Q's, because my fortay is mainly with the CD4E.
But yeah, I think your right about the bent fork. Do notice if your shifter is loose? If so, that could play into it as well. If the rubber gromets for the linkage wears out, this sorta stuff has been known to happen. Not sure if I have heard of only 5th and reverse though.

I will have to do some searching on that!
As for the syncro's grinding... Well, it depends alot on not only how a person drives the car, but the fluid that is used in the tranny and the syncro's themselves.
There are updated synco's avaliable that are less prone to wear and alot of the people have been switching to Redline MTL fluid with great results in situations like yours. I have read a lot of posts were people would complain of 3rd gear grinding and just switching to the Redline MTL stopped it.
If you are pretty sure about the bent fork (shifter not being loose) then your best course of action would be to get your hands on a set of the new shift forks (have roller bearings) and the new syncro's... and well... bite the bullet.
Here's some part numbers and prices that a fellow CEGer put together...
-- Shift Forks --1-2 Shift Fork - YS2Z-7230-BA - $19.24
3-4 Shift Fork - YS4Z-7230-AD - $22.22
5-R Shift Fork - XS8Z-7230-DD - $21.05
-- Replacement Synronizers --1-2 Syncronizer - F8RZ-7124-AA - $45.41
3-4 Syncronizer - F8RZ-7124-BA - $35.54
3-4 Syncronizer - F8RZ-7M000-BB - $39.65
5-R Syncronizer - F8RZ-7124-CA - $37.52
5-R Syncronizer - 97ZZ-7124-CB - $39.73
-- Syncronizer Blockers (Snap Rings) --3rd Gear Snap Ring (4th & 5th) - YM2Z-7107-EB - $7.01
3rd Gear Outer - F5RZ-7107-A - $28.03
3rd Gear Inner - F5RZ-7107-DA - $10.05
Man I hope that helps you out a little. Shot me a PM, with your e-mail address, and I will shot you back the spreadsheet that this guy put together. It is really a great piece of information to have.