<human>: Could you distill the essence of the text into 1-3 sentences?

Background: I am in a good financial situation. I am 22. 2 months ago I bought a car from a dealer. A 2000 Avalon. We agreed on a price before they knew that I earned 58k a year. I think they assumed that I had a rich dad or something. I got a good deal. The dealership, during the credit check, found out my financials, and pushed HARD for a more expensive vehicle, pulling out all tricks out of the book to insure I would not get the 2000 Avalon. I got the car anyway, after calling the dealership out on a bunch of bullshit. They fully checked the vehicle, and changed oil, tires, timing belt, etc. I got a warranty for 1k miles.

Fast forward 2 months. Getting an oil change because I put 3k miles on the vehicle. Merchants(national auto services chain) tells me that the dealership must have changed the drain plug, and that its leaking. They wont remove it for liability reasons, ask me to call the dealer. They use the term "piggybacked". I know nothing about cars, so this is all jibberish to me. Merchants tells me that if they remove the drain plug, they might mess up the pan, and that would cost hundreds of dollars.

My instinct tells me the dealership knew exactly what they are doing, and are being douchebags.

So my question: What is the best course of action here? I could call the dealer, and tell them that if they dont fix it, I will post a bad review on every website I can find, and not reccomend them to my friends. To the mechanics of reddit: what are your thoughts?
<bot>: drain plug fixed by dealer, pretty sure they did it on purpose to get more business from me/screw me.