THis is such a common problem with the 04's (not sure about the other years).

Mine does the same thing, it sticks when its below like 55 degree out. From my understanding the grease swells when its cold. I've heard that completely cleaning the tracks out and all the grease then replacing it with a better quality grease can possibly do the trick. I've heard that White Lithium made by CRC does the trick.

I'm going to try this once the better weather gets here.