Hi.

okay, change the gear box oils at the same time, so drain the boxs,Filler/level plugs on the drivers side. ( lots of posts on site re this) undo the 4 bolts holding on the prop to the gearbox output flange, pull away and suspend on a piece of string/wire out of the way. (Long time since done this one).

Put truck in gear, chock wheels, remove the large nut, may have split pin to secure as well, from end of output shaft. pull out the output shaft.extract old seal, you can buy a tool for this, but I used a bent screw driver, work all around seal, a bit at a time, till it pops out.Do not scratch or damage the housing.

New seal , oil well, oil the seating area in the housing, hold new seal in place , with out damaging the sealing lip on the output splines, and gently tap with a soft faced hammer all around the circumference, or you could use a large 1" or 3/4" drive socket and tap gently intill it is home. Note before you remove old seal, note how it fits, re depth. Oil the removed section of the output shaft before inserting it. Bolt up, refill gear boxs with EP 90 and grease the prop shaft uj's while your are under there.

As said a long time since having done this, but I hope you get the idea, and find this some help.

Rear/front output shaft oil seal available from "Milners" top of page under "Parts Dealers". Similar to this.

http://www.milneroffroad.com/categories.asp?cID=10584&p=2

Suggest you consider purchasing a "Service Manual" available on site as a download or CD. top of page "Service Manuals". A very usefull item !!