Do I have to take off the cover the drain the old oil out? I can't find a drain plug. If I take it off, do I need a new gasket or just use RTV?

 

Yup, take the cover off, and the fluid falls out.

The fill plug is in the pass side of the center section about halfway up.

Make a point of looking at your gears while you're in there, count the teeth or find the stamping on the edge of the ring gear, help stamp out useless "what gears do I have" posts in advance with equally useless "codes" replies.

I usually use just the "tubular style" of gasket.