Re: '78 evinrude 9.9 how much oil in lower unit?
Takes less than 1/2 quart, I filled mine twice from a quart bottle. Buy the BRP synthetic gear case lube availlable at your Johnson/Evinrude dealer(IBOATS), or Sta-lube makes gear case lube for outboards, try a marine hardware or NAPA.
Be sure to get new nylon sealing washers for the fill and drain plugs, and torque them as they will leak if not tightened correctly.