I'm pretty sure goatman did it, but I haven't seen him around for a while. His posts might be useful, and his email may still be available and active.

As I recall, parts were hard to find, but he had a few sources who he found and he eventually finished it.

The 1st gear shifting (especially from a full stop) might be a dragging throwout bearing making the clutch keep spinning - next time it does it, try shifting not quite into reverse and see if you can hear the dog teeth grind in reverse. If they do, the clutch is sticking for some reason or other.

If I were going to rebuild/replace an M46, I would personally get an M47 Mk2 and do whatever was needed to that. They have heartier bearings on the output shaft and no overdrive to need new seals every 50-80K miles. I think the Mk2 eliminated the need to overfill the trans too, but I'm not sure.

Cheers!