there are also a square (our ref. RPG-722.6-SQ) and an oval (our ref. RPG-722.9-OV) rubber plug gasket available. Unfortunately we cannot specify which one has to be used for which application / serial number.
the plugs are not in our overhaul kits - they have to be ordered separately.
Please check also our Product Identification Data Sheet: "IDS-722.6/9/725.0-bell-housing-plugs"