My daughter does the accounts for a garage in California, and her boss, the garage owner, said that they'd had a few Minis in, all with belt tensioner problems. He said "We'd better have a look at yours, the parts don't amount to much, and it means expensive noises if it fails". She regards it as a perq for working there, repairs done for free or very little.
I wondered if any mechies here had noted this problem with the Mini (Cooper)?