Fellow 18V50 Owners, We have seen several failures of O ring part # 354 1628 and 354 414 on the LT cooling water lines to the charge air coolers. The O rings appear undamaged when removed apart from a permanent flattening of the ID where they contact the pipe. These leaks have all occurred at very low hours (2500-5000 hrs). I suspect that a better grade O ring material would have a longer service life, but do not know what material was originally used by Wartsila. Does anyone out there know what these O rings are made of, and have any of you switched to aftermarket Viton or other materials for longer life?