Rubber window mouldings dry out and become hard after years of use. The moulding around your car window is exposed to direct sunlight and heat, which causes it to deteriorate faster. Rubber moulding can be restored by cleaning it with a sponge and soap and then applying a conditioning product.
Clean the window moulding with a mild soap solution mixed with warm water. Dishwashing liquid works well. Mix equal parts soap and water, and then use the lint-free cloth to clean dirt and residue from the window moulding.
Saturate the sponge with the rubber or vinyl conditioner. A sponge works best for its gentleness and absorbency. Thoroughly wipe the window moulding, working the conditioner into the rubber.
Let the conditioner set on the moulding for 10 to 15 minutes, then apply another coating. Leave your windows down for four hours following the second application.
Rubber/vinyl conditioners are available at most auto parts stores. If you cannot find a suitable product, use a vegetable-based cooking oil (almond oil is mild and works fine).
Most rubber moulding can be restored, but if it is dry-rotted, the trim will have to be replaced.