O-ring to seal the rear drive to the swing arm (MG# 90706584)
Moto Guzzi V7 Sport, 750 S, 750 S3, 850 T, 850 T3, 850 T3 California, V1000 I-Convert, V1000 G5, 1000 SP, Le Mans, Le Mans II, Le Mans CX 100, Le Mans 1000, 1000 SP III, 1000 S, California II, California III, California 1100, California Jackal, California EV, California EV Touring, California Aluminium, California Titanium, California Special, California Special Sport, California Stone-Metal, California Stone-Touring, California Classic, California Touring, and California Vintage models
For this O-ring (MG# 90706584), I've never seen any refefence to a UNI O-ring code within official Moto Guzzi documentation. When I measured it, the cross-section is clearly 2.62 mm. The ID, however, is more difficult for me to assess. My best guess is that the ID is 58.42 mm. Theses measurements correspond to UNI O-ring code OR 3231.