I changed my antifreeze last summer on my Yanmar 2GM20. This winter I noticed antifreeze in the bildge. I went to the Yanmar dealer in my area, he told me right away the it was the drain cocks, he said run the engine then check for drips from the tubes coming from the cocks. Sure enough, they were dripping very slowly. He told me that he has had failures on new engines with the plastic drain cocks and he recomended just installing a brass plug, something he nomally does. I had him order new drains anyway, they took almost all winter to get here. I normally take my boat around the harbor several times in the winter to run under load at high RPM's but didn't because of the leaking cocks, I did run it at the dock but lower RPM's. When they arrived we looked at the new cocks and they were all brass, no more plastic. He called his supplier and they told him that Yanmar had redesighed the drain cocks and made them all brass and that was why the long wait. Brass is always better than plastic.