Well with a little research the Tecumseh oil PN appears a 1 Quart, 15-50 WT synthetic oil. Mobil One 15w50 synthetic could be a cross for it, also Kawasaki 99969-6501. Now both these does have a zinc additive. Now I have needed to order the Tecumseh oil so I don't know its actual specs on rather if it contains zinc or not.
Also this might make sense. 1.25 to 2 inches down from top of the hole.