'90 E30 rear end woes... I think I need a new diff:( need advice.

[many944s]

Well, starting about 4 weeks ago, I started to notice what I thought was rear wheel bearing noise. It was a "purr" coming from the rear of the car that faded when cornering to the right. I have worked on several other E30s that the culprit was indeed a wheel bearing, HOWEVER....

When I tore down the rear end of my car to remove the half axles I was at first discouraged, as it was IMPOSSIBLE to get the half shafts out of the hub splines. I did notice though that there was no slop or noise from the bearings when I turned them by hand.

THEN, I turned one of the output flanges. The differential has an audible "noise". It is not a tic, clunk, click, it's more of a "catching" sound. Instead of turning smoothly you can feel it "catch" slightly almost every degree you turn the flange. It feels kinda like turning the shaft on a stepper motor, where you can feel each coil pass a magnet, that slight catch-release-catch release. So, I a thinking it is an output flange bearing. Sound reasonable?

Next question: I have found a used diff locally to put in the car while I repair the original (as it is my DD). This temporary diff is from an '87 325e and is a 2.93 open diff. Is this the same diff that would be on my '90 E30?

Thanks for any input!
-Nick