Brian, My RC 81 needed a full resto but was all original and pretty clean. With shipping, it cost me around $9k. If you remember, the Penn auction had 3 RC 81's that were original unrestored and they went from 11,500 to 19,000. No need to bother looking at the inside of the door unless you REALLY have to. You've been in this business long enough to tell what's original and what's not. If he's had it for over 25 yrs. and all original, I'd feel comfortable with it. If it was a fully restored machine, with no prior pictures...it would be necessary to document the inside door. Remember people, these machines were taken to the scrap yard and didn't hold much value until recent times. Do what makes you feel comfortable. It's a lot of money for a machine ,yes, but how often do they come up for sale? I know you've always wanted one so just do it already!
You won't regret it!
JB