Check engine + transmission problems = NOPE!

I really just want an opinion on a decision I made.
So, I’m a 25 year old short white chick who knows nothing about cars. I just have common sense and I’m not too lazy to actually RTFM.

February of 2013, I became the second owner of a 2001 Chrysler Concorde. Carfax says previous owner bought it new, spoiled it, everything we perfect.
My check engine light has been on for about two weeks. I got three different opinions that all pointed to a solenoid in the transmission. I also heard the words “clutch” and “lock-up” but it’s an automatic. All three agreed that to fix this problem, the transmission would have to be removed and re-built. You can’t access the transmission from above or below, so the engine would probably have to be removed as well. Fuck me, right?
I used this information to get EIGHT different quotes. Four of them were Chrysler certified shops. Numbers were from $2500 to $4000. Fuck that. I still owe $4216.33 on that car. With no equity to pull, and I’m not gonna borrow my CCU’s allowed 80% against it to fix it.
I drive home my new 2001 Lexus LS on the 22nd.
The dealership gave me $6200 for the Chrysler, freeing me entirely of the loan. Having a 620 credit score, I can afford a little bit of a hit. The dealership asked about the check engine light, and I told them it needed a new solenoid, the truth, but I didn’t tell them anything about the transmission.

Upon receiving the diagnosis of the check engine light, the questions were all the same. “Are you having problems shifting? Is it making any unusual noises? Are the lights or radio failing?” No. Everything is completely fine. HOWEVER, on the same day the light went on, the drivers heated seat quit working. (Coincidence?) I cycled through a few tanks of gas, had everything inspected and refilled, and everything is FINE. I asked one mechanic if he could reset the check engine light. My logic was that if this is a genuine problem, it would come back on, but if it was some bullshit, it wouldn’t turn back on, but the mechanic wouldn’t do it. Is there some legal obligation there?

Questions:

  1. Was this a good course of action?
  2. Can the dealership nullify the deal because I didn’t mention the transmission?
  3. Why did they give me $6200 for a FUBAR $3000 car? (I do have a guy in a high place in the industry, and I want to know if he had any involvement.)
  4. Why would I be having clutch problems in an automatic, or is every mechanic an asshole?
  5. None of these mechanics charged me a penny. Could it be my guy in the industry, the fact I have titties, or something else?
  6. Any advice at all is appreciated. This is my first car, and I want to learn from what happened.