I's it normal for gasket to go bad at the bottom of the Glass?

I have a 2006 Sebring Convertible. The answer is "yes." It is rubber and it will eventually dry out and disintegrate, chip or peel. I used it on my window rubber and it feels like new. Both my doors were making sounds when the car moved. I eventually discovered it was the rubber around the doors aging. I bought something from Amazon (originally from Germany) called "Nextzett 91480615 'Gummi Pflege Stift' Rubber Care Stick - 3.4 fl. oz". It's a small bottle but goes a long way. You apply it to the rubber around your door (clean it off first). This "miracle" stuff helps restore the rubber so it doesn't make chirping or rattling sounds and it helps with leaking (as a result of the rubber getting old). I swear by it. There is a similar kind of bottle available from MoPar but it costs about $50. I urge you to go to Amazon and read the very favorable reviews about "Gummi Pflege Stift," which translates into "Rubber care stick."