[KCMike]

I have used mineral spirits to clean the dial face. It worked well. Try a spot on the writing that will not show just to be sure it won't rub off. Don't use water. I believe the 70 and 90 are the same. But the dial assembly might not be. You would then have to drill out the rivets and use small bolts and nuts to replace.
I did that on a model 70 and bought a replacement from here for it.
http://www.radiodaze.com/dials-plastic-or-phenolic-30/