I don't know if it's exactly what John was talking about, but here is a trick I learned from my dad who is a mechanic.
While you have the pan off the car, brace under the lip with a piece of lumber or a small faced hammer, and then tap around the holes on the top side with a ball peen hammer.
The idea is to try to flatten out the bump that is formed from all the prior installations pulling the flange up toward the trans case.
I seem to remember being told that it was good to have it slightly pushed beyond flat, just so that it would pull flat when you torqued the bolts in. Don't go too far though, as you would cause a leak then.
If this isn't what you had in mind, John, please teach both of us something new!
