hi mate, have you used hi strength threadlock on the mounts and all mounting screws/bolts? also have you superglued the engine-diff brace screws in? if not this could be your problem.you will have to use a blowlamp or gas soldering iron flame to get them off again! but thats reliable largescale methods mate
where nare you in uk? if you keep having problems bring it down to a local race meeting and we'll sort it out.