The 3.64lsd in my 535 5 speed got damn loud about 1 week ago. I pulled it this morning; the action is very rough when turning the input flange by hand.
There is a differential rebuild shop in Rancho Cordova that may get the opportunity to rebuild this unit. It happens that I am now about 12 miles from Bavarian auto recyclers, in Rancho Cordova. They have a bunch of e34's, but I'm not sure I care to spend the $600 the kid answering the Saturday phone quoted, for a used diffy.

A little disclosure; I moved to El Dorado Hills from Bellevue last August.