Re: O'Day 30 Yanmar YSB12
Geez... been busy so this is a reply to a really old post.
Yes. On that old YSB, if I remember correctly, you can remove a top plate from the block and it will reveal all the passages down around the cylinder and into the head. It would be a messy job but could be done provided that you have good access from above.
Make sure your water impeller and cooling lines are not the problem first.