Just another headsup
I ordered O-Rings from McMaster Carr that match the dimensions of the Yanmar cooler ORings.
I have to say I see no difference in texture or feel. Theses are also Bun-O Rings which are a reputable company. They are spec'd out as a sealing gasket w a hardness of 70A.
These are a 10 for $9.95
Yanmar are 23.00 ea