I had pretty much the same problem with my 70 Dart with the K-H disc brakes. Master cylinder was always wet and fluid low. I tried making the spring clamp tighter, replaced the gasket with an NOS one that I had, but it was always wet. I even tried lightly sanding the top of the master but no difference. I finally emailed Richard Ehrenberg of Mopar Action about this problem. His response was immediate and straightforward, the cylinder is defective and must be replaced. Once I replaced it, no more problems with leaking.
