The Story
It comes to a point in time where you are no longer able to buy parts for your bikes. In this case my 1986 Honda CB350 SG I could no longer buy the airbox rubbers. This became a problem when I tried to reinstall the airbox onto the carbs and was unable to with out the aid of 2 other people and a lot of swearing, sweat, and tears.
The Process
After a lot of attempts to get them soft, which included boiling them, using a hair dryer and WD40 some more permanent was required as these were fine until you had to get in place, and the time it took meant they were cold and hard again and impossible to fit.
The more perment way is to use a chemical reaction with a mixture of Wintergreen and Isopropyl alcohol.