I want to understand that he took the pump off because sometimes it works and sometimes it does not. And he did not do it for maintenance. So if the pump works sometimes, do not invest time in repairing it, as it will soon give you problems again. The black liquid indicates that the inner SEAL or perhaps the bushing protecting the rotor is damaged. You can apply grease as a lubricating agent but do not use oil. But I insist on the uselessness of such an action because soon, it will fail again Regards