Window Gaskets
Call the manufacturer direct. I did the same last year, and they supplied new "T" section rubbers as an up-grade to the original round "O"-rings. These can be purchased by the foot, and seem to work much better than the originals.Cleaning the old rubber out is a thankless task, but a rag with acetone and a small dowel helps.Once you have installed them, try wiping them down now and again with WD-40 or similar silicone-based lubricant. This seems to help them keep their resiliance, and extends their life.Good luck!