My guess is that this is a UV problem. Garaged vehicles appear to be less susceptible as with vehicles operating in temperate environments. Unprotected rubber/vinyl seals will breakdown and loose elasticity over time. With use and large temperature extremes over the seasons, expansion/contraction of the inelastic seal is likely to cause it to detach and become decrepit. Has anyone tried using an exterior UV protectant like Xtreme vinyl spray as preventive maintenance? Sunscreen might work too.