RE: Help with Motor ID!!!
First off, are the devices diodes or capacitors? If they're in fact diodes I don't know what effect they would have, but nearly all brushed motors need capacitors for electronic noise suppression. They have no effect on rpm. Look closely at the cans; does one have a sleeve on it? It's bee a bit since I did much with brushed motors, but as I recall the sleeve will reduce rpms. On the other hand Mabuchi's aren't exactly built to the closest tolerances and the speed difference may simply be a normal variation due to differing tolerances.
Walt