Hi my mk3 Ford Mondeo has a problem. When I got it, it was burning a bity of oil but then it started running on 3 cylinders, my garage tried a new set of plugs but that only worked for a day, was told that one of the plugs was oiling up? been quoted £500 to repair it, New piston rings, timing belt etc? Does this sound right? Just want to know that if I spend £500, my car's going to be fixed. Thanks in advance.