Black death on the glow plug tip

I have installed a while ago the SurlyoldBill mod on My glow plug controller and for a couple of months it showed #2 glow plug dead so I finally got some time to remove it. I drove the van to a few places and on the way back I started the removal process and the glow plug seemed stuck but a lot of back and forth with lots of wd40 managed to drive it all the way up and yet it would not budge out so I continued to turn it, spray wd40 and crank the engine even rev up the rpms maby times until I finally pulled with a pair of needle nose pliers, all together it took 3 hours of negotiation. I cleaned it very well then sprayed compressed air and then crank the engine then more compressed air and finally when I was ready to install the replacement I realized the two I had were bad glow plugs I kept for reasons I do not remember, however the ones I had in hand were clean so I out some antiseize on the body and threads and install it until the one I ordered from europarts arrives.
I noticed the tip of the glow plug has what looks exactly like black death on it and I'm confident this is what was keeping it from coming out. I also did an injector leak test since the engine is cranky whenever I drive a few miles then try to start it after a few minutes, it never does this at the first start/crank of the day. I took a picture of the results and I cant see what is the problem with it yet.

Thanks for reading.

What happen, no thoughts?