Been a while since I updated this, but have been flat out working and haven't had time to do anything about it. Until today.
I have been keeping an eye on Ebay for the servomotors, and last week came across a "OEM VW GTi Leather Drivers Seat skin" with some pictures - can not find it now, but it showed how the parts of the OEM seat cover fit together, so today I had a go at pulling it apart. SUCCESS.
There are three "hook" fit plastic tapes (not velcro). These are two plastic tapes - one on each seam, and the idea is they interlock - kind of like the way the VY ute tonneaus fasten (if you know what I mean) - if you don't, there is a pic of one side of it here:

There is one of these seams on each side, and one on the base of the seat. Start on the bottom of one side to loosen it.
Inside there are two clips that retain the rear cover of the seat (one on each side - see pic 2) - these need to slide off towards the centre of the seat. You should now be able to lift up the rear cover completely. Underneath there is a peice of slick backed foam - this just prevents any of the lumbar mechanism from catching on the leather. At the top of the lumbar frame the seat cover is again held on with two small clips over the wire frame - these slide up and then you can remove the piece of slippery foam. The cover I just held out of the way with the seatbelt (flipped up).
Underneath is the lumbar support mat (oh, and a bit of foam at the base too - hope it isn't important cos its in the boot)

The lumbar support mechanism is a complex beast, but quite clever at the same time.
There are two motors - an up/down, on the right hand (airbag side in Aus) and an in/out (for lack of a better description) (LHS - centre in Aus). The wire hanging loose in the middle is the "up down" and goes to the RHS motor, whilst the wire on the left goes to the motor on the LHS motor, the third wire on the right is a fixes length one and is used to provide leverage to the back of the seat. As it is compressed the frame moves or bows out and voila, lumbar support. It is this RHS motor that was not working for me.
So I set about removing the servo-motor, and had to drill the rivets on the mount out from the wrong side. If you were to remove the seat (which I will have to do when I reinstall the servo-motor) then it would be possible to drill them out from the outside.
Once it was out, straight into the shed for disection. As soon as I open up the case (three rivets drilled out) I can see what the problem is. See if you can:

So the wheel is what winds the cable up - not the greatest design IMO as it has failed where the hole to hold the cable in place is. Gonna try and craft one out of alu - shouldn't be too hard - and will update on how I go.
Failing that, I now know what the problem is, and know I can get the parts at least and exactly what I need. Can't believe how much they wanted in labour to replace this (took me 30 minutes to remove seat cover, remove servo-motor and re-fit seat cover).

Oh yeah - this is also useful information for VW Golf GTi Leather Seat Cover Removal too.