Took the driveshaft out of the 90 and it poured out a little fluid, put the driveshaft back in and noticed the seal was a little worn and half broke off, now its leaking. How hard is this to change? What is this seal called?
Thanks!

 

rear seal for ds on transfer case small screw driver and hammer

 

^^^ x2 , its stupid eazy

 

You pop the seal out with a lady's foot bar or a screwdriver and A hammer.Becarfull not to gouge the housing when removing the seal
Clean the bore were the seal will go.Put a little sealer on the out side of the seal and drive in straight.You can use a board or even a scoket.Just make shure it goes in the same depth.
Also check the shaft for groves made by the seal.If there is a grove on the shaft you can fix that by not drive the seal in as far so it rides on a smooth surface.0.30" differance will work.
what we have here is how to change most seals.Inspect everything and go slow.
Good luck.