Under the truck the other day removing the winter salt and sand deposits and noticed oil sprayed on the bottom of the chassis at the tranny rear seal.

At the same time I've noticed a bit of rotational drag when accelerating slowly from a stop, almost like an out of round disc and dragging caliper.

How difficult is the seal to replace, and are special tools required?

Is there anything else I should be looking at that might have caused the seal failure or may be causing the drag I mentioned?

Truck has never had front diff replaced but rear diff was done 6 years ago and rear yoke and seal done last year (no evidence of leakage there).
I did also have the same seal replaced about 6 years ago.