Hi Mike,
Two set screws are what is supposed to hold it on. The corrosion had pretty much fused the arm to the motor shaft. Even when I cut it off (at the shaft), I couldn't get the wiper arm off. When I installed the new one, I put some white grease on the shaft and inside the fitting on the arm. It may make it easier the next time.
A while back, someone posted about a battery terminal tool that would work to help pull the wiper arm off. I tried a search and didn't come up with it. Anyone else?
I reset the sweep to 110º before reinstalling - works much better on the window on our 25. Finding just the right position for the arm so that it parks at the side of the window is a trial and error solution. Allow yourself plenty of time for this project... I figured an hour or two to pull and replace the motor... figuring time allowed for a stiff drink, some swearing, having to dive under the boat to get the wiper arm I dropped, more swearing, the cutting, the bandaging, pulling, more swearing, grunting, stopping to catch my breath... about 2 days +/-. :crook