I have all 3 of these engines and would not let them go for the prices you are asking. It might be worth your time and effort to get them running properly- I'm sure they would sell for more.
crazydoug
The Stuart 7A and 8 run just fine now on low air pressure, there's nothing wrong with them. The James Coombes is probably okay just tight. I don't sell my engines to make a profit, don't need it and this is just a hobby.