Do yourself a favor: after installation of any rubber seal that's going to be exposed to the atmosphere, go to a drug store/pharmacy and purchase a bottle of gylcerine. Use a cotton swab and smear the gylcerine over the rubber, then use a clean soft linen cloth to rub into the surface, and remove the excess. Rub it into the rubber surface well, and do it twice if you have to. Glycerine is very viscous and will attract dust if not carefully rubbed into the rubber surface. Try not to get it on any glass; if you do, use a window cleaner to remove the residue.
Reproduction rubber can crack in less than one month—particularly where it's under a stress, like at the window corners—especially if you live in an area with high ozone content, such as Los Angeles.
If you notice a white chalky material on the surface of your rubber products, particularly when first purchased, it's supposed to be there. It's an antioxidant that's placed in the rubber when it's mixed and is doing just what it's supposed to do: bleed to the surface to protect it from ozone contamination. It's easily removed with dishwashing soap. When you remove it, apply glycerine. Do yourself another favor and don't use commercial silicone-based protectants. Silicone is not the answer ton rubber/leather/vinyl surfaces. Most of these products are petroleum based and aren't compatible with silicone. In fact, they will harm rubber over a period of time. Do the gylcerine routine at least once a year, It's no different than protecting your paint by waxing it.
Zymol Seal is a glycerin-based protectant that, while expensive, is recommended by many detailers. It will not heal cracks, but does seem to give the seals more body and suppleness. Use it sparingly—a little goes a long way! Clean the seals first with a very mild and weak solution of detergent. Remove all the dead rubber and solution. Let it dry thoroughly. Apply the Zymol by working it in with a foam-tipped swab. If you seals are very dry, try leaving Zymol on the surface and let it soak in for 2-3 days before wiping it off.