Geoff,
This may be totally unrelated, but I just had a similar problem with my car. It started with difficulty getting it into reverse and then the Shift Lever just completely disconnected, as in NO GEARS! I took the shift lever off (3 bolts, depending on how it’s cut away, should be accessible from the top) and when I felt aroung in the oil, I found a NUT. and the “saddle” (for lack of a better term) that the Shifter fits into was just floating around free in the oil. I found the threaded end of the Gear Shift shaft by feeling around and was able to get a socket in and reattach and tighten the nut. Now works perfect! I don’t know if this is the same problem, but I know it’s the same transmission so check it out. The nut being just loose would definitely make it difficult if not impossible to get the car in reverse.
Good Luck
Rich