Digging through my older hobby stuff I came across my old .049 Cox Sandblaster (not RC). The front tires were hardened with age. One rear tire was still like new, but the other rear tire was really shrunken and hardened up. I've tried soaking this rear tire in WD40, vaseline and ethelyne glycol (anti-freeze), but not luck. Next try will be automatic transmissioin fluid. Anyone have any other ideas?

If I can't fix it, I'll have to retrofit some other tires (and possibly wheels) to it, but I would prefer to restore the original tires if possible.