Bringing this back to the top asking tighted1 if I misunderstood his post about that 'O' ring bulge.

If that filter housing/filter isn't seated properly, could some portion of the filtering system be bypassing the nominal flow pattern/rate? Just a thought/concern.

I did review the job I did on mine, that lip on the cap (on the 08's) do sit over that top housing case. The lip of the cap should be snug on the aluminum case housing. There should be no portion of the 'O' ring visible, or 'bulging' out. If the other 4 years (07 down to 04) are built the same then anyone who has an 'O' ring bulging out at the top does not have that 'O' ring in the right position, nor is the cap properly seated in the housing.