Re: what kind of oil ?
Howdy RByfor.<br /><br />Your gearcase uses 90W hypoid grease/oil. It is available in tubes or bottles labeled for outboard engine lower ends.<br /><br />I don't remember if the '73 6hp has one or two holes.<br /><br />If there are 2 screws remove both to drain, then pump fresh oil into the LOWER (drain) hole until it overflows out the UPPER (vent)hole. Put the upper plug in, with a new gasket, then remove the nozzle of your tube and put in the Lower plug with a new gasket.<br /><br />If there is only one (drain) hole, you must lay the engine on her side to drain and on the other side to fill. Slower, but it worked for my 2HP.<br /><br />Good luck.
