Well it finally happened, time for a new clutch in the '91 535i and we decided to do the upgrade to a lightened e28 flywheel along with an e28 m5 clutch and pressure plate. Actually the only reason to change was the release bearing that had started making noise, so we got all the parts (new guibo, center support bearing, bolts, etc.) and pulled the sucker apart. The clutch disc still had a good bit of material(!) but the pressure plate fingers were all tired and the release bearing was shot. There were a few minor problems, such as a rounded head on a bell housing bolt, frozen pressure plate bolts and the exhaust being a bear to get back on, but we prevailed. Once things were back in place my son asked "when was the last time we changed this thing?" I pulled the service records and after some quick subtraction, the answer: 290,417. Car now has 385k on the clock (first clutch was done by the dealer for the first owner).