That depends if the leak is coming from there! you may have a hole somewhere in that case get it off and sort it, i had one and it kept making this fartin noise at mid revs...fookin annoying, and you do lose a little power as you are not getting proper flow
Mine made a leak there when I first installed my header. The collector approached the cat at a slightly different angle and it forced the donut gasket to sit cattywampus on the carbon buildup, leaving a gap on one side to let it leak.
I unbolted the cat, cleaned the carbon off (gently) with medium-grit sandpaper, and bolted it back together.