[mikethedruid]

I use black RTV and paper towel. The RTV turns into actual rubber when cured. I spread a thin amount on the cone around the whole damaged area, being careful to brace things from the other side so as not to increase the damage. I spread a thin amount on one side of the paper towel patch cut large enough to cover the entire damaged area with about 1/4 inch on each side beyond. I then put on the patch, RTV side to RTV side, and carefully press it into place, again, providing support from the opposite side of the cone. Let it dry over night and you have a good, strong repair. You could use a coffee filter instead of the paper towel, but, since I drink instant coffee, and don't use coffee filters, I use what I have.