Saw an article about using a couple readily available chemicals to soften old carb boots, or any hardened rubber pay. Mix 2/3rds Isopropyl alcohol with 1/3 Wintergreen Oil (Methyl Salicylicate). Soak the parts for a day or 2 and they come out soft and pliable, albeit stinky for a while. Use gloves with the Wintergreen Oil. It'll soak into your skin and turn into Aspirin.
