Re: MD2B - Shift detents
If you take the gearbox top cover off (the cover that houses the quadrant) you may see what is wrong in there. It is held by 4 bolts.
It is not a lot of work and you are not disturbing much when you take it off.
The detent mechanism is very likey to be on the quadrant housing somewhere, and it may be easy to see when you take the cover off.
If it is on the gear shafts, then it will be a fair bit more work, but not impossible to fix.
Volvo spare parts for that gearbox are very expensive indeed. I have seen a single gear priced at $3000+.
Sorry, I could not find an exploded view of that gearbox on the web.