Front brake master cylinder help

I just recently put the front brake master cylinder from my 01 YZ250 onto my 98 YZ125 and it has no pressure, i've gone through a whole bottle of brake fluid bleeding it trying to get it to work but has no pressure, sometimes it has very little pressure almost nothing at all. When i finish bleeding it i press the front brake lever and see little air bubbles coming from the top between the master cylinder and the top cap where the black seal from inside goes. I know im bleeding it correctly and it worked fine while it was on my other bike could it be that the seal is messed up? Anyone got any ideas, tip, suggestions etc.. Any help would be apreciated, Thanks