The timing belt is supposed to run dry. No belt dressings or other sprays are called for. Not sure what "silicone" your mechanic used, but hopefully it won't cause problems. All gear drive systems have a characteristic whine of some sort, and the timing belt is no exception, although it typically subsides as hours accumulate and the belt breaks in. In our shop, we don't consider a minor, low-pitched belt whine on some of these to be a malfunction, so it would not be repaired at all, unless loud or objectionable. In that case, we would inspect/replace the belt and/or pulleys as needed. As for the warranty question, if you are within the warranty period, you should ask for any repair service to be covered under warranty, unless it's a result of things that are beyond the manufacturer's control (for example carb varnishing due to poor fuel, etc.)... BTW, to get a repair of any nature on any OB for only $50 is not a bad price. Our hourly rate is $75