It's been a while since I've had a 400 apart, but I seem to remember the filter being able to "float" a little on a single retaining bolt. The siphon tube section of the filter that plugs into the case has a sleeve-shaped rubber seal with ridges on it, so the filer doesn't have to be rigidly held into place. The 350 filter is held on by two screws, and is attached tight to the valve body. Not so with the 400 for some reason.

Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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