p/s pump o-ring

[dennyo]

noticed a little oil leak on the p/s pump and decided a new o-ring was in order.When I got the tank off the existing ring was made of plastic, tapered in shape to match the port and had a flat cross section not round like a ring would be.I ordered a replacement ring from a dealer and got a regular o-ring as a replacement.Has anyone else seen a plastic ring on their pump before and will the round ring seat ok in the port?Any help is appreciated.