Before you even drop a cent with the seller towards purchasing this car get permission of the owner to take it in to a shop and have it inspected. Even if the cost of getting the car to a shop and the inspection costs you a hundred bucks it's money well spent.
I doesn’t matter at this point how nice the interior is; what’s the underside like. With you saying that it needs a little body work and the gas tank is leaking that tells me rust. If it’s just cosmetics; bonus that’s easy to fix; but what if it’s structural as well? As in frame rails and this being a partial uni-body car the floor pans; which hold this car together. You also mentioned that you think it might need an alignment. With the age of this car the front suspension and steering may need a complete rebuild.
I’m not trying to rain on your parade but I just hate to see someone jump into something and then have their dream of a nice older car be smashed. Yes almost anything can be repaired/rebuilt it just depends on how deep your pockets are and how far you’re willing to dig into this pocket.
If the person selling the car doesn’t have anything to hide or they may not know about the car; they shouldn’t have a problem with you having it inspected. It’s not going to cost them anything other then a bit of time, but it could save you a whole lot of grief. Regardless of their excuse for not allowing an inspection I would walk away, there’s always another car.
Dan.
Canadian "EH"