Softening the old air intake boots. Boil in water for 30 minutes then put in 50/50 isopropyl alcohol and wintergreen for 24 hours. Wintergreen is becoming harder and harder to find. This is meant for horses.
Methyl salicylate - I used to buy it at the drug store. Don't get it on plastics! And don't sit on a rag soaked in it like a buddy did. Blistered his butt. In the Navy, we sometimes used it as a penetrating oil.