While taking apart apart the lower unit, I’ve reached an impasse. The online manual I have says I need special gear housing cover tool
#(91-30291A2) to remove the gear housing cover. (Looks like a notched ring, with the arrow pointing to one of the notches.) Here are pictures of the cover and the tool.
I found the tool on eBay for $75, but is there a cheaper homemade way to get this ring off?