O-ring, Dr. Oligo XLc, used on the bottom of the window assembly to seal against the top of the synthesis plate/rack. This O-ring is Orange in color and made from soft silicone material. This is the second version of seal that came on the instrument. The first version was black in color and made from a different material. This new version can be used to replace all (old or new) Synthesis Plate Top O-ring Seals.