O-ring for sealing the dash indicator lens to the dash (MG# 90706076)
Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models
Buy these O-rings
The size of the O-ring (MG# 90706076) used to seal the dash indicator lens to the dash is approximately 8 mm ID × 1.8 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 93125K23 (7.8 mm ID × 1.9 mm wide) will work well.
Here is one place where the inch equivalent will work perfectly fine. Just use the Dash size -011 with a Shore Durometer (A Scale) = 70. These are 0.301 inch ID × 0.07 inch Thick and will work perfectly fine. McMaster-Carr part number 9452K19 works great.