Herman Miller Aeron Office Chair size C lift does not work

This is a Herman Miller Aeron ergonomic office chair. It has a black mesh seat and back with adjustable armrests. It's a reliable choice for long hours at a desk. The chair is fully loaded with forward tilt. However the lift stoped work and I am not handy enough to fix it nor I have the time to work on the chair. Looking to sell for $450 flat. Easily a $600-700 chair used. Just need to replace the pump