Master cylinder lid leaks, why?

[77BBGMC]

I replaced the master cylinder with a rebuilt unit. First time doing this and didn’t realize that I was supposed to bench bleed the master cylinder before putting it on. I have bleed the brakes a couple times with a vacuum type unit. Brakes work great but I’m leaking brake fluid from the top of the master cylinder. At first I thought I had too much fluid, I removed some of the fluid, repainted a few items and assumed I was good to go. I drove it a couple times and seemed to be okay, next thing I know I have fluid leaking again. I replaced the lid and rubber seal with another new one and I’m still struggling with fluid coming out between the seal and master cylinder. Anybody have any ideas what would be causing this? It's getting a little frustrating, ruined the paint and powder coat on a few parts...twice.