RE: Shockwave 26 Brushless.
Hi Rich,
The black dust is from the propshaft and inside bearing wearing away at eachother, or if it's lubed too ethousiastically, it's muck from the bearing and propshaft mixed with grease.
Judging from the picture, there's no flatspot for the grubscrew on the propshaft, I'd file one on it.
While you're at it, see if you can straighten out the damage from the slipping grubscrew.
If the driveshaft slips, the boat doesn't move, hence there's no flow in the cooling system, so both ESC and motor will tend to heat up.
If on top of that, the motor is running at half throttle, you run the risk of a fire, due to overheating the ESC.
If the propshaft it smooth at both ends it should be able to slide in/out from the inside and the outside, whatever works best.
Regards, Jan.