I received a bad part. What should I do?

i'm the seller,i think mark wanted a new part for used price.i was honest in my description of the box,it came off a good friends truck that he'd owned for 10 years and drove great...you move the steering wheel and the wheels moved with minimal play as i described.i would not have wasted my time pulling and cleaning it if i thought it wasn't good.when i inspected it for mark i just held the box down on the desk and twisted the pitman arm....it rolled silky smooth lock to lock....being that i had drove the truck i didn't see any reason to check any further nor did he specify for me to check any further.it was in good working order when i shipped it to him ...for a used 32 year old part.i have tried to settle this with mark by offering him 45$ and him keep the box or a 60$ and him send it back which is the full price of the box minus shipping.i have sold a lot of parts on here and other places and this is the first complaint....and hopefully the last.its hard to please everyone all the time but i do want to resolve this where we both can be happy.i always try to describe my parts as good as i can,and i feel like we both are at fault here somewhat and neither should be made to eat it all...i will go as far as sending him the full 60$ and he keep the box to save him from shipping it back....i think that is fair.i just saw this post this morning and had to put my side on here.thanks guys