Originally Posted by olhipster1

Diff should not be overtightened...ever...
you should be able to re-use...might need to rebuild and examine...

Did you sand/polish the plates (with very fine grit sand paper). this will make a huge difference for the quality of the diff.
once together...build up then install in car..
put car on a stand...and hold one wheel and break the diff in..a few minutes each side..this should help the diff ball seat into the plate...should score the plate slightly.
Run the car under load...then recheck diff.
With the Schumacher diffs ..make sure to install the set/locking screw correctly.

should last for quite a while after that.