Ok dtw, that's why I asked if I was missing something. Is aly oxide not a form of corrosion? Maybe it isn't. I was just pointing out that if it's wet O2 we are concerned about-$450 later I certainly am-the cyl seems to be the first place it will manifest. And the powdery stuff seems more likely to get past the restrictor in the O2 lines and is more likely to block up the solenoid closed as opposed to the good ol' rusty flakes blocking it open. Given that I have heard of more solenoids on the Prism failing closed, I don't know the answer, hence the post... And thanks for the detailed explanation of the magnetic field/sealing issue Brent.