O-ring for special top cylinder nut on V700 models (MG# 90706119)
Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models
The size of the special O-ring (MG# 90706119) used to seal the top cylinder nut on V700 models is 12 mm ID × 3 mm wide. Viton O-rings are best, but Buna-N work just fine and are a lot cheaper. Make sure to purchase an O-ring that is sufficiently soft...something with a Shore Durometer (A Scale) = 70 is great. McMaster-Carr part number 9262K266 or McMaster-Carr part number 9262K41 works great.