Condition is the main factor in determining price. Location is second because it determines rarity. The owner of a motor with "only a few" missing parts may have to be reminded that those very parts are commonly missing and almost impossible to find except on a complete motor. The Elto’s Atwater Kent ignition system is the most efficient ever devised, but did have some problems with bearing seizure. As a result new parts have been made to fix these problems. Likewise rubber tiller grips have been duplicated for many antiques. Replacement fiberglass lower motor covers have been made for those aluminum ones frequently lost on the green tank Mercuries. Rubber water pump impellers have been duplicated for many old outboards. Manufacturing a flywheel like the one for that model has been done, but is a very expensive procedure. . . 🙂