What is a rear pinion seal?
On the rear axle, in front, where the drive shaft connects to the rear end. That is the location of the pinion and it has a seal to keep fluid from leaking and keep dirt out. No idea about the cost of labor, but parts should be around 30 bucks (seal, oil, & gasket) I can do one in a few hours. Get this fixed quickly, its a LOT cheaper now than when the rear end wears out.