PD,
I was going to suggest the brake fluid trick also, but I don't know if Dot 4 would have the same results. We used to use brake fluid to shine up the tires on our cars. Supposedly, after time, it would leach all the stuff out of the rubber that allowed it to flex, then cause cracks and extreme dry-out. I never owned a set of tires long enough to see if that was true, however....
