Re: lower unit grease on sea king (chrysler) 6 hp 1970
It is not grease, it is hypoid extreme pressure oil. You can buy the marine oil at any auto stoe and some K mart and Wal Mart stores.
A 16 ounce tube will probably be sufficient. You are looking for marine grade lower unit lube. It will be someplace around 85-95 weight. You can use regular or synthetic.
Keeping the engine vertical, you remove both plugs and drain the old oil. Then while the engine is still vertical, you clip the end off the tube, push the tube nozzle into the lower drain, and squeeze until oil comes out the upper vent. With the nozzle still plugging the drain, replace the vent screw, then remove the nozzle and replace the fill screw.
Let the engine sit vertical for about 1/2 hour to let the air rise. then remove the drain and quickly insert the nozzle. Remove the vent and top off the oil. Then replace the plugs as above.
If perchance your six has three plugs, two will be on top labeled fill and vent. Drain the oil by removing all plugs, replace the drain plug and fill through the fill until oil comes out the vent. again, wait 1/2 hour and top off.