One theory I have that is that this often occurs in cars that are Garage kept. When we moved into a house that had a two car Garage as a kid, my Mom's 83' Cadillac developed it's first stinky climate control about two months after we moved in (86') The car was kept outside before that and never had an odor. Since then every car we have owned and garaged has developed that smell. I think it may play a role