So I got the replacement (lifetime warranty) today.
More solid out of the box and the cap actually fits!

I think the issue is the same
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The point where the plunger goes in ~ if it isn't fully out (think foot off the pedal direction) then there is some play... micro gap type play.
I believe its just a bad design!, but might have an idea... the plunger isn't adjustable. Nor is the pedal's distance from the floor.
And when installed, the plunger is a mm or 2 too long. So it is pressed ever so slightly when sitting.
I added a couple washers and a custom gasket and got it so the pedal has to be pressed 2 or 5 mm to line up with the plunger. Thus, when my foot is off the pedal (ie. when parked overnight) it should be fully extended ~ and thus no gap.

Maybe...
I'm still going to make a cover for the fuse box because I don't know if its gonna do it again!