Gooday Nick, replacing the rear drive flange oil seals is straightforward and cheap. There are two oil seals and two sealing caps involved, (one of each for each side) and they are in stock at any good aftermarket VW shop. Just explain what you need to the friendly salesman and he'll know exactly what you need.
Then you need a workshop manual.
Just remove the rear axles by undoing the CV joints, then remove the drive flanges to expose the oil seal.
It is best to replace the oil-seals in situ, without removing the threaded side-cover, as this will disturb the adjustment on the differential bearings.
Having said that, you can remove the side covers if you really have to - but seek more advice from the forum first, as there are some complexities involved. None are difficult, but you have to drain off and replace some of the tranny oil and mark the position of certain components before removal.
For the short job, good quality allen keys and a medium-sized pair of outside circlip pliers are needed, and and oil-seal remover is handy but not essential.
It's a bugger of a job to do while lying on your back, but a cinch with a hoist or over a pit.
The job is similar on a Superbug, T2 Kombi or T3, so any experienced VW mechanic could do it in a few hours. An old fart like me would take half a day. Give yourself the whole day or even two, and then you can clean out and regrease the CV joints while your at it.
I reckon the CV joints should be repacked once a year, because they cost an arm and a leg to renew if you ignore them, and develop a very embarrassing clunk that sounds like Thor is killing a swarm of redbacks on his anvil.
This is especially true if you have done, or are contemplating, a desert trip. Sand is the enemy of CV's.
Before you order the parts, check the CV's for axial slop in case you need to order new ones. You will probably need 4 new rubber gaiters as well. Don't try and save a few dollars if they look brittle, crazed or torn. I use LMM grease and a paddle-pop stick to repack the CV's. Others use a turkey-baster or pay more money for the dinky little sachets sold through the VW shops, which are easy to use and carry the correct dose.
If you like brain-teaser puzzles it is good to totally dismantle each CV to clean it and check for galling and wear, but just remember - the way to re-assemble them is not the obvious way. Read the book.
Large cable ties serve as an excellent replacement for the metal gaiter clamps.
The Lithium/Molybdenum grease is filthy stuff so you'll need some old clothes and plenty of rubber gloves and kerosene or diesel for cleaning.
While you've got the rear axles out, it is a good opportunity to spin the rear wheels to check for rumbles or slop in the rear wheel bearings.
Go for it.
Roger Beetle Bayley.