Depending on your car color you may get away with what I did. Autozone sells inch and a half wide black detail tape. 7 bucks a roll and it does both sides. I peeled all the loose old rubberized covering put the tape on it and it looks very nice. It is not a 'purist' fix but my friend who notices details hadn't noticed. The price is cheaper than new rails and the tape has been on for over a year and still looks great. My car is garage, but it has made it through the tough winter no problem. I can buy a lot of tape over the years at 7 bucks a pop if I ever need to replace it.

Hi dino

There's something about roof strips on my site, with info about fixing them up without forking out to the dealer for new ones. Go to body -> roof straps. Also something re. the "mystery of silicon protectants" which may or may not be relevant for roof straps (- that is one of the current mysteries!). The thread of discussion included there is particularly relevant to roof straps, so may be of interest to you.

Dino,

Others have had the same problem in the past. IMHO, any rubber, plastic or vinyl part that goes unprotected in intense heat will eventually dry out and crack. Like any part on your car you can order new strips from the dealer. When installed, protect them (and your rubber bumpers, window trim, door/trunk seals) with any of the many detailing protectants on the market.