While I wholeheartedly believe Tesla
should cover this... for those that are worried about their rubber seals (I'm not convinced Tesla didn't use substandard rubber), Krytox is a fantastic rubber treatment! (disclaimer: I do not work for, nor am I associated with, Krytox, or whomever makes/sells it in any way)
However, it's expensive and 'interesting' to apply!
To see posts like this makes me glad I live in the northern climate, as well as keeping it garaged! To the OP... I would try to escalate this and see if you can plead your case that this is 'unacceptable rubber degradation'. It looks to me like it's just a case of serious UV damage - but I'm not an expert!
Good luck!