If it is one of the electric shift models, the lower unit gear lube you need is called Premium Blend. It's a little thinner than the regular stuff. I think OMC (Evinrude/Johnson) stopped making the electric shift models in the early 70s.
Also, when you change your lube, always use a new seal (around drain screw) as they are meant for a one time use. They are about 60 cents to a 1.00 at most places I think. (Although I have found that some dealers like to double the list price on small parts to make it worth their while.... I won't mention any names...but I don't do business with these folks any more out of principle.... Don't get me started.....)