sh!te Rowlers U have no luck lad, the cheapest option is 2 get an OE seal kit from VW and replace the seals on the OSR, about £15.00 per side, once caliper is removed check to ensure the piston bore is not damaged, any small scratching can be took out with a little elbow grease, eg with 1200 sandpaper?
If the above is no use you are talking £145 a side for reconditioned Mk3's or £30 a side form a local scrappy, if going for option 2 i would still get a seal kit and repalce them, piece of mind if anything.