If it is an Ontario car, (or not in one of the deep south states), I'd not be concerned about the rear window. It seems to have been an issue where them temps get very hot and the sun bakes the window all day in the sun.

I'd be looking to determine the state of:
original documentation
any known modifications
oil leaks
tranny leaks
rock solid roof operation
evidence of undue wear/damage to the roof (material)
both keys
glass condition (esp. windshield)
body panels/plastic needing attention -parts are $ and may be hard to find
documentation of repairs by previous owners

Otherwise, these little gems are in many regards, mechanically bulletproof. Things that are broken, worn or not working (electrical/mechanical operation of lights, radio, seats mirrors, spoiler, tires, wheels and trim, etceteras) will be pretty obvious and you negotiate the price accordingly with a plan to get them fixed or buy spare parts. The only other things to note are that often there can be "road rash" around the bottom of the car that may separate the car into being either acceptable or unacceptable. Condition of the paint and finish is personal and therefore negotiable in the price. My suggestion is to find a nice one and be prepared to pay a premium to get it. In the end, it is worthwhile.

Temper alot of what I say as it depends on whether this is to be a "toy", a second family car or a daily driver. Given that you are probably in the salt belt and won't likley be drving the car from Dec through Mar at a minimum, you'll probably be somewhat **** about owning it. What ever your inclination - make sure to drive it on the highway and the street and get it onto a hoist for a look see.

Good luck! There are a lot of great members here who will guide you if you've done some searching/reading on the forum first. As someone said - get a big bowl of popcorn and deveote a night to reading what you can.