Great collection of Classic's Zig, I see your missing the Tornado ?
As for Skid Marks problem? Why did you strip the paint ? I would have just cleaned it up with warm water & dawn dish soap. You could try this to see if it cleans up the yellowing? Use a napkin in water and littlely clean surface & dry with non-abresive cloth. The pitting of the plastic, how much & where? You might be out of luck. You might have to fine a repop?