The car is a 1988 Mk2 GTi 8v in the middle of being done up to go back on the road. I've been doing the brakes at the back while I had the rear axle off for new bushes and some Hammerite but when I started to reconnect everything I noticed the brake pressure regulator (or bias valve) is leaking fluid, and not just a wee bitÂÂÂ

1. Is there a repair kit/replacement seal available? (nothing on ETKA about but my version is old).
2. Any tips on things to watch out for if I have to change the whole valve?
3. Is GSF the best place to buy a replacment from? (GSF seem to list it a £46+VAT if I'm looking at the right part!)
Any help gratefully received, thanks