I did not have to install a woodruff key. My kit came complete, all I did was mount it on the bike. I have two brand new kit's still in the box, there's no woodruff key lose. I dont think there is any damage, you may have to back that nut out a bit. How much black powder is there??
I just pulled my cover a few weeks ago for the first time. I have just over 3,000 miles on it and there was very little powder. I hope you did not eat your clutch up.