I noticed a small drip from the impeller, so I checked it and it is fine. I tightened the brass fittings and the Allen bolt on the bottom and there is still a tiny drip coming from the rear of the housing. Is this where the lower water pump is located, and is this indicative of a more serious problem? I replaced the upper pump years ago and regularly replace the impeller if any 'legs' are broken or missing.

Thanks