My shearer small bores leaked from the orings right out of the box.. All i did was ordered 4 OEM orings. They are bigger then the ones that shearer uses. I took some emery cloth and sanded them to fit snuggly into the flanges.. (They will not fit w/o sanding) No more leaks and no messy sealer.
The seal will offer a bit of resistance. But on a trail bike id say they are a must. You do not have to kill the nut. I always just tightened it until i had no play, then killed the jam nut.
From what i remember i always had little residue of fuel in my carb boot when i ran a box. If your jetting issue is down in the lower rpm range, lean out your needle and try that before you change mains.