April 6, 2013:
I fired up the outboard to run/clean it some more. I figured that letting the gas/Seafoam mix sit for a week or so would be good and would really clean the sludge out. I guess I was a little too right.

It started right up and ran great for about 40 minutes. Then it started slowing down. By the time I hurried out of the boat's cabin and to the outboard it was just above an idle. It tried turning the throttle up and down, but it just slowed down and died. I could not restart it. With the cruise getting closer and outboard shops starting to get backed up, I called around and found to my surprise that the Tohatsu dealer could get to it in a day or two. It took a couple hours off work Monday morning and delivered the motor to them.

They called me on Thursday when it was ready and said the problem had been the carb needed a good cleaning. My amateur guess is that the Seafoam loosened years of crud and sent it to the carb, which couldn't send it on and clogged. The repairman said the motor now ran “like a sewing machine” and he had adjusted the idle down a bit, but high enough that it didn't die when he shifted it into gear.

I put the motor back on the boat and was happy when it started on the first pull. Now, what's next on the To-Do list?