I am embarrassed to say that even with 8+ years sailing C-27's there is still stuff to learn.
Wes and I were contemplating his spotless engine locker last weekend. Wes mentioned that he had purchased an M-12 maintenance kit that included an air filter. I clearly recalled, for once, that when I put Windrunner's engine back into service 4 years ago that I checked the air cleaner and it contained an expanded metal ring. I thought that is was a pretty course filter and reassembled it. Challenged and curious Wes suggested that we check his out. We did and sure enough there was a crumbling foam element mounted on the expanded metal ring in his air cleaner. We installed the new element.
Yesterday I checked windrunner's air cleaner verifying that my recall was correct. Last night I ordered the element from:
https://www.westerbeke.com/category/M-12/5399ADA2DAF73A26740BF6CA
part # 301049 ELEMENT EA $12.40
Smoother Sailing thanks to CPYOA
regards charlie