Mike, I'm getting old and forget stuff. Another reason the screw comes loose is that some people try to adjust the diff by tightening or loosening the diff screw on the TA03 diff. This is not the proper way to adjust the diff, The diff screw should always be cinched down tight or eventually it will work loose.

I think I posted it in the tutorial so you probably knew not to touch the screw after the diff was built.