Check this post out...
http://www.elcovaforums.com/forums/s...ad.php?t=27428
Scroll down and see the H3's swim-en. Wonder if thses guys had your problem. But then again..they might not have been underwater as long as you.
Also..maybe our resident Hummer Engineer "F5FStop" will check in and advise you on the tank vent ..etc.