My ATSF has always had GREAT SMOKE, never a problem. Of course, it arrived without a battery cable. Lionel Service put a battery cable in the engine for me.
If we combine my engine and your engine, we could get one engine that works perfectly well, … but probably not for long.
Buying an engine today is a "crap-shoot". These are the two words most often uttered when the engine does not work. The only consolation is that I will "out-live" my trains.
If your ATSF #3759 should have drive shaft issues, at least you now have an idea of what the problem might be. Good luck and best wishes.
Sincerely, John Rowlen