mag 9 has about 6 months of usage at most. mag 18 does not have nylon screws. but you can get them at home depot. both pumps have very little wear. they look brand new.
Head, they're 2 different pumps. Too many different aspects to decide which is better. They each have their own application. You should start a thread or do a search. The F/S forum is not the place to ask these types of questions.