Well, I locked in the grub screw last night w/ some threadlocker and tested it out this morning. It's holding up right now. I was talking to a friend who suggested the mesh between the pinion and spur may not be fitting properly and causing vibration to make the grub screw come loose. Anyone heard of that?

I also bought some "good" tools per the LHS.

Anyway, I'm running the car through all my batteries this afternoon. We'll see how it holds up. I'm ordering a new pack of pinions and starting over.......