Gentlemen,

It's been awhile since I read all this thread so bear with me if someone else has already made this suggestion. My son has been literally sweating this problem out on his favorite 300TD and after going through everything, he comes to me and informs me that he's found a sight crack in the plastic pressure tank. Then I realize that he's been fighting an unwinnable battle.

So if any of you are having a similar problem, do a pressure test on your system first. If it fails holding pressure, look around the filler neck on the plastic tank. Bet you'll find a crack. New tank, new pressure test, pass, problem solved.

Ben