The retaining self tapping screw for the heating element around circulation fan has come loose on my Zanussi ZDA 45B oven .949700044 SER 54904272 The fan WAS vibrating. Hole has worn and screw simply turns and will not tighten. Is there a solution ? Maybe a bigger self tapper but have not found one to replace existing short and stubby. If so details please and where can I get one.Many thanks for any suggestions. At present screw removed,fan not vibrating but I guess iis only a matter of time.