How bad is this rust?
 

I just passed on a '80 SC that had rust on the driver bottom door jamb under the rubber (2" x 4" section that my finger pushed through). Looks like it was coming from the "inside out". There was also a spot of rust at the rear top of the driver door jamp coming through behind a screw.

Also, headliner was stained from water through the sunroof and I thought that this might have drained and collected in the door jamb.

How worried should I be of this so far? If the car passes PPI how worried would you be of rust in this area?

There is at least Twice as much rust that you can not see.
I would move along unless the price reflects the rust condition.
Are you Handy with a welder?
Professional rust repair cost add up very quickly very Labor intensive.
Do you have any pictures ?

Pass. There will be others even if the price is reduced because of the rust. What you described sounds like major problems once you get into trying to do the repairs.

Yes it will be major body work. You can have PPI, but if you include price of the repair, can easily get another rusat free example.

Does it have the tensioner upgrade?

What kind of exhaust does it have.

Does it have history of service?

Pass. There are too many nice SCs out there to buy one with a rust problem.

I think it's a matter of your time, skills and money. If you have a welder and some skills then maybe it's a project worth taking on. However, if you are just looking to buy and drive, then you should probably keep on looking. I agree Joe that if you can see rust, then you can be assured there is more that you can't see.