Air in rear brake system

[Fojyie]

I have a '80 CBX and have rebuilt the brakes (more than once), I thought successfully, but I keep having to bleed the rear brake. The rear master cylinder wasn't in good shape: pitting. So I honed it mostly clean except for one really deep spot. It is about where the rubber rests in the MC. I wonder if air is sucked by here into the system. I can bleed it and all is well for maybe a dozen uses, then it fades away to nothing. Bleed it out, all is well, but it fails again. Guys, these brakes are killing me. I've had issues front and back, thought I got it right and this reappears. I measured the rear MC and diameter seems okay per spec, but don't know for sure. Got any thoughts?

[steve murdoch icoa #5322]

As EMS pointed out the other day for a similar problem on the front brakes, a little teflon tape on the bleeder valve MIGHT solve your problem.

[Fojyie]

I have been using telfon tape on the bleeders. Good reminder. It must be sucking air by somewhere. There are no leaks or fluid showing either.