Lubricating lower unit to a Wizard rototiller

Inherited an old Wizard Western Auto rototiller from the 70s.
It does work. But how does one go about lubricating the lower unit?
Has no zert fittings but I did find what I did take to be the equivalent of an oil fill screw. Is this one of those things that is usually filled at the factory, sealed, and usually you don't have to worry about it again? Or is it something that you're supposed to check each season? And if the latter is the case what type of oil or lubrication would you use for something like this?

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