I use Hylomar
. It works very well on all gasket surfaces where oil pressure exists. It does not dry but stays tacky (non-setting). This makes it very easy to clean up with rubbing alcohol the next time you disassemble.
If your oil pan is lightly warped you can "glass it". A large piece of flat glass with some 400 / 600 grit wet paper taped firmly down is a good base to start sanding that oil pan flat. Lightly press the pan in a figure 8 motion onto the paper. You'll soon see the high / low marks on the pan. Continue to sand till the entire piece is flat. This will not take long. Just remember... keep that pan flat