I think this topic has been covered thoroughly by every one elses suggestions/opinioins, but I thought I'd share an anecdotal experience I had when I bought my X5 from a used car dealer.

When I bought mine, it was a lease return with about 38,000 miles and the price was phenomenal. I think it was roughly $14 under Kelly retail and about $9k under Edmunds. I found it on Autotrader minutes after it was posted, and by the time I got down there there were 3 other people already looking at it. I basically took one look at it, drove it around the block, and said I'll take it. Now, I realized what a liability it was at the time, but the deal was too smoking to pass up and figured I could afford a couple small things that went wrong because of how well I bought it.

About 3 weeks later, it sprung a little coolant leak, and then a couple days later the climate control totally stopped working. After reading up here, I found they weren't uncommon issues (expansion tank and FSR), but they weren't things I was happy about paying a mechanic to fix. So, I called up the dealer I bought it from and simply said "Hey Martin, I'm really enjoying my car, but I've had a couple small issues. Did you know about these or have a mechanic look at it?" I told him what they were, and he said well to be honest he didn't have his guy look at it, but he told me to bring it back and he'd have his mechanic take a look at it because his rates are way cheaper than what I would find elsewhere. I had a backup car to drive so I left the X5 with him for a few days.

He called me and said everything was fixed and to come pick it up. So I came with my checkbook just assuming he'd hand me an invoice. When I showed up, he handed me the keys and apologized. I said no problem - how much? He said he just has an account and wasn't sure what the $ damage was. I said ok well how can I pay the bill if I don't know what it is? He laughed and said not to worry about it! I couldn't believe him and honestly try to pay but he wouldn't accept it.

All I'm saying is that I was clearly aware he had no fiscal or legal responsibility in the matter, but I approached him amiably and he responded in a way I never anticipated. You never know what the outcome is when you go back to dealer, but I think it definitely well worth it to try. It doesn't matter IMO if you have "legal" standing or if you signed as-is docs, from an ethical standpoint what happened to the OP sucks and a stand up dealer would make it right (or at least be of some assistance). It never hurts to try!

__________________
2001 X5 4.4i
2002 Honda S2000