O-ring for sealing the 80 mm speedometer and tachometer gauges to the dash (MG# 90706746)
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# 90706746) used to seal the 80 mm speedometer and tachometer gauges to the dual instrument dash is approximately 75 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 9262K316 will work well.