Looks yummy.
It is a leak but not the rear main. It looks like the transfer case driveshaft seal.
Easier to fix then the rear main seal.
of course there is always the option of watching the fluid levels and seeing what happens.... that is what I did to my 3.slo before i ended up fixing a leaking seal on the transfercase, rear axel seals and intakegaskets.... and a bunch of other stuff.... the truck was still very much drivable but looking at fluid leveles ever tank of gas or so got real old real fast.
so i just fixed it