Rubber boot for the oil pressure sending unit
Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models
Thanks to Charles Hamer for sending me this information in a private communication:
For the little rubber boot to cover the oil pressure sending unit (MG# 12717600), NAPA has one that fits like a glove.
NAPA part number 727302.