Thank you all for your replies, I greatly appreciate it.
We tried the hydrogen peroxide & removal of plastic food dishes, but a few of the dishes have made it back into circulation. Will try removing them for good and see if that helps.
Benson does not eat wet food at all. He never ever has...
Our cat Benson has been taken to vet twice, given eye wash, an extended round of Prednisolone 5 MG, and two rounds of Neo Poly Dex Opth Ointment. Yet the black crusty stuff just keeps coming back. He has been treated with Neosporin, but will rub his face until it's all gone. What is this crust...