Just bought this boat with a Mercruiser 1983 model 470 170hp and had some cooling problems, seems the impeller was shot so I replaced the water pump body, impeller, gaskets and water pump base. Now when I fill the reservoir with coolant it leaks from the lower unit with the engine off. Could I have improperly installed the water pump? Prior to the repairs had no leaks just overheating and coolant backing up and over flowing from the coolant recovery tank. Any help would be great!