Cadillacs are over priced headaches that don't even warrant all the praise of a luxury car...This is one of the reasons why GM is going down the tubes. These cars are an overpriced gimmic for getting rich can't do it yourselfers to keep pumping money into the Gas Guzzling Machine...BUY A HONDA! VOLKWAGEN! Lincoln Towncar is much better!

I can answer generally for all luxury cars that have gotten old, whether they be Mercedes Benz, BMW, Cadillac, Lincoln, Acura, Infiniti, etc.
They all reach a point that they become too expensive to repair. Repairing an old luxury car is as expensive as repairing a new luxury car. As a basic example, many years ago my parents owned a Cadillac Cimarron, the cheapest Cadillac made at that time. One day, the alternator went out on it. A typical rebuilt alternator at that time cost around $65, but for that car the rebuilt alternator cost $400. The manufacturers (both cars and parts) figure that if you can afford to purchase the car, you can afford the premium repair bills. The size of the repair bills doesn't go down as the car gets older.
An owner who is trying to unload an old luxury car at a rock bottom price is looking for a sucker who doesn't realize this yet to take the money pit off his hands at a price that is higher than an automotive salvage yard will pay for it.

The heater core may be leaking / faulty - not familiar with Cadillacs, but normally it is located inside the car, behind the dashboard (glovebox) on the passenger side (near the blower motor). This may be something for a mechanic to diagnose if you are not familiar with automotive heating/cooling systems.

This isn't a solution but a suggestion. If you can afford to get you another vehicle get rid of the daewoo leganza. The car was always in the shop and parts are more expensive than some luxury vehicle. Also to find parts is a nightmare and sometimes you have to order from south korea. I was very happy when my engine died because now I could get a better car without all the problem and expense. From 2005 to 2011 I spent over $6000 dollars on repair/service that was regular service/maintenance(excluding oil changes,tire and brake changes and schedule maintenance).

dealer item only or goto a salvage yard and get used?

This is common for Cadillacs and GM's in general. The security system GM used since the mid 80's is the most common failure on their vehicles. The cost to fix is rather expensive and trying to isolate the problem is even harder. Ive had great luck with just bypassing the whole entire system perminantly. This link explains the problem and offers pictures and DO IT YOURSELF solutions.

http://vatspasslockpasskeysecurityhelp.yolasite.com/

Go to www.passlock2.com and you can get rid of that problem or you can put a new GM ignition switch and lock cylinder in it.

there is a part know as the blower module on most gm vehicles. It is located on top of the blower motor housing.; unplug it and see if the blower shuts off. They had that problem with a lot of the cadillacs. The module was located under the hood next to the firewall. I do not know where yours is located, but I hope this helps.

Sounds like you have the common problem with GM 6.5 diesel. The PMD ( pump mounted driver, the black box on side of injection pump is failing when it gets hot, cools down just a bit and restarts. Eventually it will leave you stranded.I would suggest replacing entire pum for warrant purposes, Sorry for bad news but I have seen many of these go bad. GM actually extended the warranty on these pumps to 10 years or 100,000 miles. This was not commonly known, even by dealers. It will be an expensive fix. Good luck. Please rate my answer

GM put some batteries under the back seat. Not sure about cadillacs IF its not under hood go ahead and look there.

i found them at gmbushings.com didn't have to buy the whole knuckle