I use an actual gasket on the differential because it makes it easier to remove (trying to remove one thats been stuck in place with a whole tube of RTV is a pain, imagine how youll feel if you have to do it on the trail). The trick is to coat the gasket with chap-stick on both sides before bolting it together.
The drive flange gaskets almost have to have some (just a little) RTV or they will leak. I glue one to the flange, then another to that one, then the face of the flange gets, you guessed it- chap stick. A little 90w will work in a pinch, the point is to provide enough gasket thickness so it will seal and then keep it from permanently sticking to the hub so it can be reused when you do not have a spare on hand.