Good info above this post. I'll add that I clock the seal haves by maybe an 1/8" so the seal halves do not line up exactly with the cap parting line.
I also clean the metal surfaces thoroughly with brake cleaner prior to massaging the sealant into the metal to insure good adhesion between the sealant and the metal surface.
I also use a small bead of sealant along the sides of the seal retainer and block parting lines on the outside of the two parts.
On a somewhat related issue, make sure to use the correct length oil pan bolts in the seal retainer, they are shallower, as they are not drilled and tapped as deep as the rest of the oil pan bolt holes on the block. A buddy found this out the hard way when trying to chase down what he though was a rear main leak.
