is there a guide to what prices are good for a SSEi and what to ask the seller about the car?

I think I may sell my SLE 40th and look for a SSEi and I am in the dark when it comes to what years are problem prone just as what years are better than others and also what are the price ranges these years fall into. Also when a person looks to purchase one, what are the correct set of questions to ask about the car, I would hate to ask a person the obvious questions and not know the if this or that has been replaced on the */C?
I think you get the Idea of what I am asking.......

I now have my second '92 bonneville SSEi and one of the things I would ask if they have checed the */C oil. If they have no idea what it is, then chances are they have not. Most mechanics do not know about it either as it is not included in the standard checkup on these cars. These */C typically run out of oil about 100K and then the */C goes out. Also, if they know to check and have checked their */C oil, odds are they are pretty maitenence savvy and have taken care of other things as well, but that is just my opinion. Good luck

Checking the */C for oil, Is that something I can do when I inspect a car?
Also when is a */C in need of servicing, are there tell tale signs or is it by the mileage amount it has?

Post moved to Gen.Chat, will get more exposure here.
In Techinfo under this post http://www.bonnevilleclub.com/techinfo/?article=22 it tells you how to change the */C oil, but it also says how to check it, its really easy.

if the */C rattles at idle then, use that as a barganing tatic....its only a 30 min fix