I think 8 or 16 oz would do a set of tires. Its been a lond time since working with it, but a little went a long way. It definately softened the rubber. The platens would get hard as a rock on the surface because of constantly being beat by the typing bars. You could not push your fingernail into it. We would wet it with the fedron and lightly (very lightly) sand it. You could then push your fingernail into it.
Hope this helps.