Standard pans I use cork. No sealer. Make sure the pan isnt bent in at the bolt holes. Tighten gently with 1/4 ratchet. Or very snug with a nut driver. if you have the ribbed deep 518/A46H style pan the thick reusable factory gasket works very well. Iv'e had the trans apart many times in my racecar over the last 11 years. Still using the same reusable gasket. The pan gets blamed for every leak. Often that is not the case.