I bought a scratched 240mm Rodagon for an 8X10 enlarger that I was assembling. I got the lens for a song and thought it would be good to test the system with. Eight months later I am still using the lens. It has an ugly 1/8" scratch (not just a cleaning mark) in the center of the front element. The performance of the lens is such that I have not felt the need to replace it. 20X24 prints are sharp and contrasty and have made me re-think my aversion to lens defects.
I am curious about what others have experienced. I know that "mint" used lenses cost way more than battle-worn lenses (the cost of a new 240mm lens is astronomical). I have decided to stop looking at the scratch. It makes me feel better about the situation.