Cork isn't my favorite but there are ways to improve it's sealing ability.
First, make sure the pan rail is flat. Often what happens is the holes in the pan get a cone shape due to overtightening. If those are not flattened, it will never seal well.
Second, never torque a cork gasket to spec. They squish out every time. Watch the gasket as you tighten the pan. Make sure that the gasket is being compressed but not too much. Check the bolts after a couple drives to make sure they are not coming loose. Ater you do this several times, you will develop a feel for what is right.
Something else that doesn't hurt is to apply a skim coat of silicone. We're talking a very thin film, not a 3/8" bead along both sides of the gasket. This helps to ensure a seal and it will hold the pan to the motor long enough for you to discover loose bolts.
Lawrenceville, GA