My SP has Stern stickers all over the boards in the backbox however, it still says Sega on the outside. So technically, Stern did indeed make SP machines.
That broken switch is readily available at Marco for $17, for now...
The key to number of plays will be the flipper button area and the Kenny hole. Both of these take a beating. As mentioned by others, the plastics around the Kenny hole take a beating and are often broken.
Certain SP parts are getting to be unobtainium. The characters on the PF (including Mr Hankey) are action figures that if you can easy get on ebay to replace any that are missing or damaged. The toilet is often broken inside the bowl and is very expensive to replace, if you can find one.
I picked up my HUO example that was perfectly clean with zero wear around the Kenny and Cartman holes for less than he is asking.