David,
Thank you for researching through all your info. The Bridges reference is great to know, that’s much less oil than it would take to fill the gearbox chambers so that helps me think the amount needed is just enough to keep things generally lubed. When I cleaned everything this afternoon the only trace of remaining oil had all dried up and if I had to guess may have been about a teaspoon worth all said and done for what I probably scraped out. My drill is like the one in your second photo with the two fill holes.