Brake Master Cylinder leaking problem.

I am experiencing the same problem as well as many others. I have filed the top of the master cylinder and got it perfectly straight with no grooves or edges and I got a new cap and even went to the extent of using silicone around the top edge to seal it. I know I shouldn't do that but I wanted to see if I could stop the leak and it still runs down the side of the master. I think an upgrade to the aluminum master may fix it, I can't see why or how it could leak after being sealed. Good Luck and if you fix it let us know!!