I will start with a new fuse as that is accessible easiest, should be able to do that be end of weekend hopefully but sadly dont have access to a multimeter so i'm going to have to assume the wiring is good. RE gearbox and internals, they are steel rather than pot metal etc as standard with a poly silenced piston so only upgrades that should be required are a fet for the contacts and any performance upgrades i might like such as tbb, hop rubber etc. Would the gearbox have produced the screechy noise before it died? I did listen to it closely and it definitely came from the motor so i'm reluctant to go fiddling in there unless i can rule everything else out. Also, if the issue was the gearbox, wouldn't loosening the screw again resume the motor activity, which it isn't.