The brake master cylinder of 531-900-922-500 fits for Ursus Tractor. The reference numbers are 50750320, 975032. The fitment details are URSUS C 360, URSUS C 360 3P, URSUS C 385. The seal material can be mounted as per your request. And we have EPDM & NBR for the seal, the difference is the fuild in the brake system.