OEM sealing crush washer used on the oil filter cover bolt. 

These need to be replaced EVERY time you change your oil filter.

Used on the following Moto Guzzi models:

V7 - All years, all versions

V85TT - All years, all versions

V9 - All years, all versions

Also used on older small block bikes: Breva 750, Nevada 750, V35, V50, V65 etc