I built a Four Star 40 several years ago with the stock plastic rods. I never noticed any changes in trim due to temperature changes, but I did notice that they started to get sticky after a couple of years. While doing a bunch of other work on the plane, I took out the nylon rods and replaced them with metal pushrods in the same outer tubes. Things move a lot more freely now, and there wasn't enough of a weight penalty to notice.