Soak it in linseed oil, you will be amazed. Let it sit over night. You can buy that oil at any hardware store. The reason I know it works is because I tried it on my Mangusta rear glass rubbers. When I repainted the car I wanted the rear glass in the hatches removed. The rubbers were beyond hard, I had to be very careful not to crack the rubbers or crack the glass. The replacement rubbers on the goose do not work very well. I soaked the rubbers with a very heavy layer of the linseed oil. The next morning results were amazing. That was 5 years ago, they are still soft today.
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