At 100k miles I took my 1995 850 in for a regular 10K service. The car was running great. Dealer told me the serp. belt had cracks and needed changing. I authorized it and they did it. Ever since I have had a lot of vibration. Worse at idle, slightly better when driving but still noticeable. Dealer then said it was from the lower motor mounts being collapsed and the engine sitting on the frame. I had them changed and it did not help the vibration. Now dealer says it is definitely coming from the belt because when they removed the belt the vibration goes away, but they do not know exact reason and can't fix it because they can't diagnose it. Any suggestions? Is it possible they replaced tensioner backwards or something like that?