Re: 73 merc 1150 help
Wave, It is real common for water to get into the gearcase via the drivesahft seal contained in the waterpump base. Metal shavings are also real common in the gearcase. I recommend you abandon your plan to open the gearcase and do further testing to see if it is really necessary. Purchase a new waterpump base and cover, plus an impeller, wearplate and gasket sets. Now sand all the corrosion off the driveshaft and pry out the old waterpump base. Install the pumpbase gasket, with some grease on it. Grease or oil up the driveshaft, oring on the pump base and driveshaft seal in the new pump base. Carefully install the new pump base so as not to tear the new driveshaft seal. Now install the gasket and wearplate. Install the impeller with it's key. install the gasket over the wearplate. Now lube the impeller vanes with oil and while turning the drivesahft CW, install the new waterpump cover. Grease the driveshaft splines and the shift shaft splines, and install the gearcase into the midsection. Gearcase and motor control should be in neutral. Turn the flywheel until the driveshaft splines aline, and line up the shift shaft splines. Wiggle the gearcase into positon, while finger tightening (no wrenches) some nuts to hold it on. When it is all the way mated, you may tighten bolts.
Now refill gearcase with gear oil and test motor on a body of water. If it stays in gear, and the oil remains clear, the motor is good to go.