Tim, I used BMW Synth. 75-140w from 12,000 miles. Very little two-up riding, and I think I'm sort of easy on equipment. The bike is a very early '99. Failure: Sounded and felt like a wheel bearing going bad in the FRONT, which it was. That may have masked a similar sensation in the back, got the front wheel bearings replaced and... What the Hell? I still feel it! Then one morning it started really screaming, five miles from the house. Drove home on the shoulder at 25 mph. The seal was still intact, when we got it apart at the dealer's in addition to the distroyed retainer others have noted, one roller was actualy turned sideways (!) hence the screaming noise. My bike now has 197k and still runs well. It's just starting to use a little oil (one qt/6k vs. none at 100k). Opinion: If I were to buy a low-mileage early K12LT I would have the bearing replaced as PM, it can be done without pulling the rear drive off for about $125-$150 and peace of mind would be worth it.