bladerunner1024

There's a TL;DR at the bottom if you would like to skip the reading

Back around December 2016 I bought a used 2007 V6 Convertible Mustang. Everything was great, I finally had my dream car and I was living large. However, eventually the car gradually stopped blowing air. For example, when I got the car the air worked just as it should. After a while, the air would cut out for a minute, then proceed to work fine. And then it would not work more than it did work. Eventually the air just stopped working all together. I replaced the blower motor resistor, a relay, and the blower motor itself. Finally I got fed up and bit the bullet and took it to the dealer in November of 2017. They texted me this: "Ok, heres what we've found. The connector of the main harness that fits to the junction box under the hood is melted/damaged on pin C1 (blower motor control circuit). It will carry voltage but wont carry the amperage required to activate the blower motor. As a first step, we can try to repair the connector, pin, and wiring where it meets the junction box. As a second step, if that doesn't fix it, we'll have to replace the junction box but at no additional labor since we have already have it taken apart to repair the wiring. We're also going to be replacing an aftermarket relay thats currently in the junction box to power the circuit for the blower motor. First step wiring repair with the diag charge included, is $575 plus tax/fees. The junction box replacement costs an additional $423.02 if its needed. Let me know what you want to do." So, I told him try the first step. He then texted and said "wiring repair alone" got it working. I picked up the car and it worked good as new, for a few months. In the past few months it's started not to blow air again, just as it was before I took it to the dealer. My question is this: do I take it back expecting to pay another $575, and have it not working again in a couple months? Do I replace it myself? Do I take it back and demand they fix it again because they fixed it and now it doesn't work? I know only the bare minimum basics when it comes to cars so I don't really know what to do.

TL;DR: Car wouldn't blow air. Took it to the dealer and paid over $500 for them to fix it because I tried everything I could and nothing was working. Now it's broken again. What do I do?
Thanks!