So i am undestanding this correctly, you used a gasket, not a RTV sealer on the perimeter, only around the bolt wholes.
I myself have always only used rtv sealer around the whole perimeter, and never used an actual gasket, and have yet to expirience a leak.
But, if a gasket is being used, a "sealer" is still needed to help it "stick/bond" so it can seal properly.
2008 Oxford White F150 FX2 SPORT Super Crew,5.4L.
2003 Satin Silver Clearcoat Mustang GT,4.6L 2V,5 speed.