OK, is there any way to rebuild the diff. I don't want to buy another used part and have it get worn down again. I rarely drift, I just want to know that I can

I chose the M42 model, specifically for the light motor. I like to go around bends quickly more than I drift and the M42 has great weight distribution for that. I'm going to be doing some upgrades to the car that will make her as quick as the 325. Right now I just want to get the drive line and suspension all set up.
Edit: Btw used to own a 325e, fun car, just very heavy. And with the older style motor set up, run in to problems first week of owning the car. This 318is - 2 months = happy camper

Except a loose hose.