Yup, and it's been that way since H-D started putting hydraulic clutches on the CVO's. Part of the black gunk is the assembly lube that's in the M/C and the actuator. It's there to protect the seals when the parts are initially assembled. Some of it is also from the inner lining of the hydraulic line. Has your fluid ever been changed? If not, I'd suggest syphoning out the gunk in the M/C (don't let any air into the system though), then fill the M/C with fresh DOT 4 and begin the process of flushing the entire system. You can do it manually, or you could use a pressure bleeder, or a hand vacuum pump at the bleeder valve. Or you could just find a qualified tech who has the right tools and have him do it.
It's a good idea to change the fluid every two years, and use the highest boiling point DOT 4 fluid you can find. High exhaust system temps can boil the fluid where the line comes hear the exhaust pipes and the trans side cover, and that will cause the incomplete release of the clutch you described.
Jerry