I found a speaker repair shop here in Minnesota that replaced the foam in some Advents at our school for a few dollars more than what I would have bought online. In and out in a couple of days.

Believe it or not, I use WD40 to clean old gunk. Then a simple window cleaner and paper towels to take the oil off when the WD 40 has done it's job. There is a solvent in the WD40 that works well. And it is after all man cologne!