What are you using to clean it?
I ask because I once scorched wort on an element and worked and worked to clean it. What I did was put boiling water in a tall container (similar to what you did), with some PBW in it, and let soak. Some would come off, so I'd do it again (boiling water, PBW).
Eventually with some rubbing, and repeated cycles of PBW, I got the element clean again.
Looks like you're doing something similar, but I'm hoping you have a better way than what I used.....