FWIW, I've had three Pels, an 800 and two 600's, for the past two years plus. They get constant use, and there is absolutely no sign of corrosion on the section ring. So my advice is to get the 400 and not to worry for two years. Put a tickler in your 2008 calendar that says, "Don't worry for the next two years." Do the same in 2010, 2012, etc.
I know

: If the idea of the ring really bothers you, consider getting a 200 instead of a 400. It's the same size pen, sans section ring. I just purchased one from Richard Binder the other day -- green marble barrel and black cap, gold-plated steel M nib, for $64 plus shipping. It ships on Wednesday -- can't wait.

(Edit: For a bit more $$, you can get a gold nib on the 200. Or... you can always buy a gold nib later. Richard has great deals on Pel nibs, regular and customized. And they're all "Binderized"!)
Either way, you can't go wrong. Have fun!