O-Ring, Y-Motion Nozzle Plate Seal, Hollow, Dr. Oligo Plate 384/768 XL.  This O-ring is installed on the top of the small nozzle plate. It should have a mix of lithium grease and baby oil applied during installation. There are 2 each different O-rings used on the Y-motion seal. This is the smaller of the two O-rings. This is the O-ring for systems with a space on either side of the center nozzle plate. This design was implemented in Oct of 2017