I had a similar issue with mine. I tried a bicycle tire repair kit but the patch was too bulky and wouldn't fit in such a small area. Convinced I was on the right track I Rube Goldberged a different solution. I took some black rubber adhesive (sorry, I can't remember the brand) and smeared it over the cracked area then I laid a heavy duty zip lock bag over the patch area and closed the door and let it dry overnight. The next day I trimmed off the extra plastic. I'm kind of amazed but this has held up for 5 years and is virtually invisible..