tiger,
What I would be looking for are the following:
1. Crack in the cover for the diaphragm(the one that covers the diaphragm).
2. Look for a hair line crack where the screw goes into the body (the jet screw).
I have had in the past had these issues and it has taken quite a few times looking at it until the light shows it up.
Some times you can not see for looking.
