In short...I tried Sierra oil filters after not finding a Westerbeke marked one
The first Sierra lasted 20 hrs before dumping all the oil past the O-ring into the engine pan. The second one lasted only 20min. The Westerbeke OEM's have since run fine. Sierra refunded my money
and asked for the side by side photos I took. It appeared to me the gasket
wasn't dimensionally the same. Never heard back from Sierra.
Note: I wrote about it in this forum at the end of 2012.