Dunno... what you see is what came to me off eBay a while ago. The motor is a perfect fit in the chassis/retainer, so suspect factory original.
Regarding interferance/shielding- is that with all Rivarossi motors, or just older ones? My main concern is finding compatible motor and worm with enough time to complete all work and document it before the clinic (scheduled to be presented at least twice in March, open to doing more if any more 4D PNW clinics/meetings? are interested!)