Renovation kit for brake master cylinder

[Niklas.L]

My Audi 100 2.3 quattro -92 is leaking from its master cylinder, between the oil reservoir and the master cylinder itself. I have just driven with it as is before, since the brakes worked fine and I only had to top up occasionally. Now however the warning light for the brakes are always blinking, before I just topped up on brake fluid and it stopped. So I think its time to fix it. I could just go to a junkyard and pick up another one, but is there a repair/renovation kit on the market one could buy?
And do you think this could have anything with the problems I've described in the thread below? The brakes are controlled partly by vakuum.
http://www.classic-audi.co.uk/forum/...ad.php?t=36240

Best regards

Niklas