You did the right thing but some people just get scared of what they can't see. So they fear the worst in this case maybe more hidden rust.
It would help a ton just to take care of any thing like that Rocker. But then you are putting more $$ into the car. It's a vicious circle.
"Perception is Reality". If a buyer sees the car as rust free and mechanically 100% sound then they are way more willing to Spend more $$$.
Most buyers don't even want to do TLC any more.
I personally believe you need to be a Mechanic to own a 40 year old Mopar. Or have deep pockets to pay someone for the little stuff that can and will Pop up. There's always going to be stuff to fix and that's just the way it is.
So You need the car to be 100% Complete to command the high Dollars.
