Brakes nightmare.....

[Enoch]

I had exactly the same issue on my car, replacing the master cylinder did the trick. My car had ABS so I had to source a m/c, I found one locally on ebay. When I first fitted it I found exactly the problem you describe. I stripped it, cleaned and used an old stock service kit, it is now fine. I think that the seals don't like to be exposed to air or something. I would suggest that it's a good idea to service a part that could well save your life anyway.
Enoch.