ORIGINAL: playerpete

this is the second time that im having problem with my diff for the blitz. I ran the truck once, and now the diff is really really gritty/sandy. I have replaced the original diff that came with the kit thinking it was defective so I bought a new one from hobby store and its still doing the same thing.. I barely ran this.. Mostly, I ran this on my front street.. I followed the assembly to the teeth as in the instructions that came with the diff.. Any ideas??? mostly, it seems like the balls are getting flattened.. But, after one run??? Thanks..