Re: 1985 Mercury (A103121) not "peeing" from tell-tail
Inshore salt marsh creek is a tip about replacing the whole pump or just the impeller, and being in there so long, you'll probably need the whole pump. In the housing is a stainless steel cup that actually houses the impeller, and a bottom plate of stainless steel that the impeller rubs on. Wear rings develop on the surfaces of the upper side of where the impeller rubs and on that bottom plate. If your pump interior has these wear rings, as I suspect it will. replace the whole pump.
All this is because of inshore shallow water, sand, and salt water going through the pump All of my work is from salt water boats. I've yet to see a water pump that didn't have those wear rings, that allow for less water pressure.
Have a hand torch standing by to heat the bolts before removing. If they don't turn out easy, a minimum of a MAP gas torch is recommended, I use acetylene.
Breaking off the head of bolts is common in salt water engines, by those not familiar with them. If using a torch bothers you, get it done by someone else, should any of the bolts not want to come out, or you break one.