Well, removing the gasket is VERY simple. I grabbed it with flat-ended tweezers, and lifted it out of the groove. Yeesh, that was rough. I cleaned it, and the groove, and greased up both with silicone grease, and replaced it...hoping it was just a dirt issue and I would not have to buy a new one. No such luck, leak continues. While I was at it, I followed all 35 pages of that link and removed, cleaned, greased, and replaced the old primer o-ring. I put the old one back simply because it does not appear to be leaking at this time. The primer button now goes up and down silently, but I have not needed to prime the pump yet, so I do not know if that function is working.
I ordered a new o-ring from the same company that I ordered the new gasket from (Trilby's Tropicals, online) and will replace both when they arrive. (The o-ring is not leaking, but it was loose and I do not need the headache of a flood at any point down the road.)
The hardest part about replacing that o-ring IS INDEED getting the motor back down the hole without pinching the o-ring at the outflow area! I finally found the right "tool", but it is a specialty item used by scrapbookers, so you will have to find your own version. Maybe a credit card, cut into a narrow strip, or something similar...