Bad differential ??

Hi folks, I havn't posted much here; sorry if this is the wrong forum.

We have a Cuda with a 360/904. (3500 stall TCI converter) Original 3rd member was a 8 3/4 open with 3.23. We bought a used 8 3/4 sure-grip with 3.55. It helped the car launch much better! However, there was a metal grinding noise, which was hard to hear over the TTI exhaust. I went under and saw wet fluid (not much) coming from the yoke area of the differential. So I yanked the sure-grip back out and out the "open" back in until I could get the sure-grip fixed.

Here are the questions,

1) does it sound like a easy fix of a new pinion bearing (or 2) and a crush sleave and a seal to get the sure-grip back "correct"? or is there probably something more severe going on? The housing is the best of the 3 possible units (489.) Note, I have NOT taken the yoke off yet to investigate.

2) I had paid $500 for this suregrip pumpkin from a wrecking yard that does nothing but mopar, and am trying to determine if I should complain or just spend more $$s and have the above mentioned parts replaced?

Thanks,

Tim Eckert