Time for a new Differential.

What causes this this is the only part of the rear-end that I can find with any serious damage or wear marks, why?
do you need to replace it? that's you're call as it really isn't doing much, but at the same time isn't just normal wear to see side gear teeth chunk like that. if the posi doesn't hold then absolutely replace it as the diff unit isn't doing its job anyway.
It's an Auburn anyway... not that good when it was new. once an Auburn posi wears there is no repair. Get into a Eaton and don't look back if you are gonna keep the 10 bolt in it.

