I'm not sure if you generally have bad luck, but I wouldn't go out and buy any lottery tickets right now if I were you.
Joking aside.
Clearly, carmax is s***.
From reading this, I get the impression that
1. They first sold you a salvage (or clearly in disrepair) car, then after it (as expected) fell apart, they
2. gave you a decent car, but with crap used tires, then after you complained, Carmax
3. blames it on an axle problem (which I find a suspicious diagnosis). One of the crappy used tires goes flat so Carmax
4. takes WAY too long to replace (the tire, not to mention the clutch issue from before) and then
5. lied to you and gave you a used tire.
Bear with me here. Sorry to be blunt, but did you test drive and fully inspect the first car? Did you have it independently checked by someone you trust? The second car? I'm fairly sure there would have been at least a couple warning signs along the way since healthy transmissions rarely suddenly blow up.
I bought a 2004 G35 6MT sedan with ~ 123,000 miles on it from a dealer I thoroughly researched, after I had it checked by a mechanic I trust, and spent over 1 hour checking everything I could myself. When I take it in for scheduled maintenance, I look over the work when they finish, and I've called them out when it doesn't meet my expectations (only takes 1 or 2 times, they usually learn you mean business). I love the car. I'm at 144,000 now. No surprises; just oil, filters, brakes, and a couple light bulbs.
I know people are busy, but I'm sure you've learned that taking some time and making some closer looks might have saved you days and headaches at this point. I'm sure Infiniti can make a lemon car along the way, but the hand full of people that I personally know that have/had owned Infiniti cars are generally very happy.
Hope your luck changes out there (and thanks for the heads up with Carmax - I won't touch 'em with a 10 foot pole

),
Lars
(let us know how it all ends up)