Stopped by the parts store and picked up a 2 arm hone. Gonna give it a try when I get home. The bleeding part is the biggest pain.

 

I'd look for a hairline crack in the mc.

 

Did honing the master cylinder resolve this issue? I am having the exact same issue on my 07 Ultra. I have rebuilt that mc and changed the brake lines. Everything looks fine, and the lever is returning completely. However, the mc slowly builds the pressure until the brakes lock up.