980 573 - It's the only marking I can find on one of my spare starters - it's cast into the housing at the geared end that engages with the engine - there's also the Gilera twin rings cast just before the number, that's it - there's a silver/chrome label but whatever was printed on it, if it ever was, is long gone.
I checked my spare starter motor and like O-B found the silver label was (almost) unreadable it is made by CEM and the last 4 numbers appear to be 2206, so I thought let me remove the one from my RC, its only 6 bolts & wont take long, after much jiggling as there is no room between the bottom of the carb and the starter idler gear it came out, but the silver label was totally blank, Looked at the Saturno but decided that was more fiddly to remove then the RC,
The Saturno parts list shows the Gilera part number as 328815 for the 350 and 328677 for the 500.
That's about it from me
Following the train of thought with Gilera's commonality of parts across the range of machines I wonder if the starters are the same body with different gearing/teeth at the gear end depending on the engine capacity, internals and compression?