[ironman]

Here are pictures from my 1200.
Yes, the a box cover seals all the way around.
The filter measures about 1 5/8" thick but it's older so the rubber seal is somewhat smooshed.
The depth of the cover is also 1 5/8".
When the filter is set in the cover you can see the flat edge lain straight across.
If you cover is not sealing at the edge I would look at the depth of the divot (for lack of a better word) where the stud hole is. Maybe it got deepened somehow and does not let the cover go down on the stud far enough??