240D MT made loud noise

[HughO]

We were driving our 1982 240D MT when we heard a loud noise under the car and thought we had run over something. Nope. Then the MT developed a whine. we turned around to drive home and she wouldn't go into 4th w/o grinding and then she started popping out of all gears and then not engaging in any gears. we towed her home. This car runs perfectly otherwise and has 190K miles on the original engine and clutch. Is this a catastrophic failure of say a main input/output shaft or what? Ideas on R&R? We have had it for 15 years and do not plan to part with her. Are there rebuilt MT? I cannot find any anywhere.