I think a bad seal would prevent the jack from raising its corner, not retracting it. I don't think your motor/pump replacement had anything to do with it unless the pump part put metal parts into the system. Maybe the valve for that jack went bad. How did they drain hydraulic fluid from the jack? Crack a hose fitting or override the valve by the allen key operator?
Ted & Melinda
2016 ACE 27.1
2016 Chevy Sonic Toad
2020 Chevy Colorado Z71 Trail Runner Alternate Toad