[Dashman]

After sleeping on it and if I had done 1 minutes worth of researching that part number, I would have confirmed my thoughts that it requires the metric o-ring fittings. Meaning a previous owner changed to that gear box. ...and reading your response, they didn't change the pump? Your "mystery yellow thing", is it like the attached photo? I think it was just a temporary plug. *Edit: The return port size is 5/8" or 15.875mm compared to 16mm metric o-ring port. Just to give you an idea of how close they match.