slow prime and leaking pipe

Your prime issue and leak are two different issues. The slow prime might be related to the suction side (everything before the pump) to include the O-ring under the pump lid (clean and lubed). There might be an tiny air leak in that suction line. See the link below. The leak after the pump at the outlet is on the pressure side which is why it's dripping externally. The picture is a bit tiny so I can't quite see what fitting was used, but it appears the adapter was glued to the PVC pipe/elbow afterwards, so you may have no way to turn or remove the adapter from the pump outlet unless you cut the PVC pipes.