Ya mine does that as well, just a little show of black every time I clean it. The middle valve o-ring that some people are having problems with isn't shreding though, it does have sign of more wear than the other but nothing serious.
I even took it off entirely and shot the gun no noticable effects like previously stated i.e. quieter smoother, so I just put it back on there. Have 5 cases through her now and am able to run 11 dwell with +- 4 FPS, and no shoot down or issues.
Gonna get a few cases of low level paint and blast through them this Saturday to try and hurry up the break in..
"success can test one's mettle as surely as the strongest adversary"