part number for oil screen gasket, O-360
This crush washer should be replaced each time the screen is cleaned.
When I was in the process of buying my flying RV-7 I went through it and found the lower rear oil filter screen hadn't ever been cleaned...in 17 years of operation. The original paint was on the exterior, the paint had not been broken around the circumference since manufacture.
I ordered some from Aircraft Spruce, the part number:
AN900-16
MS35769-21 GASKET
Lower Oil Screen gasket is what I've seen it called.