The 4 speed is the same used in 240D except that the G had a different rear diff, the tranny is usually bullet proof but not when leaks are ignored, seals are not it's greatest strength, same goes for the G's T case as well, since Gurkha uses the same T case, I have had quite a few leakages from the T case.

The bearing should not be hard to find as 240D was commonly sold in US.