1.5-2 gallons of mixed antifreeze.
Not sure what it is called, but it is easy to replace once you get the old one off. Getting that big nut off though is another story. I bet it took me 2 hours to get the nut off and 15 minutes to replace the seal. That of course was back when I had no good tools.
2000 Sahara, 3.5" Rubicon Express Lift, 1" spring spacer & 1" Body Lift, 35" BFG Mud tires, Front & Rear ARB, Rancho 9000 shocks, UCF Ultra High Belly Up