My car came with a Mercedes item called Tire Fit. I've used it twice. First time I drove it for a few months without worrying about it, then my low pressure lite went on. I tried to add air and the valve was stuck. The dealer replaced the valve under warranty and fixed the tire no charge. The second time, once again the valve went bad. I drove it that way for a year without any pressure change or problems. When I replaced all 4 tires, the dealer replaced under warranty the valve one more time. He said that technically this was not a warranty issue, but would take care of it this one more time only. He had no comments about the Tire Fit causing this though.