top of the A pillar where the metal trim and rubber all come together on the body can be a leak area. under the battery and along the top of the bulkhead another problem area for leaks. plenty of good info on here on where the tin worm lurks, bottom of the B pillar is a very busy place where panels come together inside the sills so any rust behind the side skirts in that area will be a sign of problems. Chassis legs are always my first look see, followed by front jacking points and sills. bubbles in the roof around sun roof, again lots to see on here about that. extending the drains as mentioned above is good advise, factory / design mistake there.
like all cars of this era they were never designed to last forever, some really good cars been made from something that looks like its been submarine deck cargo for the past 20 years. its always good to have at least one donor car to hand as well if possible.