Honestly, with the setup you're trying to run I doubt it's going to last all that much longer. They're just not good gearboxes.
In terms of all the things you're changing I'd be amazed if you don't constantly have some issue or other purely because you seem to be intent on slapping in whatever you can lay your hands on and hoping it works together which as you are finding out, isn't always the case.
I wish you luck.