Help! 2008 BMW x5 4.8 Engine Failure

[Emden]

So here is the story and I appreciate you all taking the time to read it. . .

On 2/9/15 I purchased my first BMW, a 2008 x5 4.8i from Mercedes of Naperville in Illinois. The car was purchased with 68,000 miles in very good condition for $21,000. A sixty day warranty was also issued with the car.
I also asked the dealer to do a complete inspection of the car, and do all the required maintenance.

Here is where the problems begin. . .

Barely a week after purchase the car was vibrating severely and was almost un-driveable. I called the dealer and asked them what to do. They said during the winter snow can build up in the wheel-well and cause problems and that I should take the car to a carwash. I was skeptical but I gave this a shot and for a few days it worked. Then I started having issues where the car would go into limp mode for no reason and shake violently again. I took the car to BMW in Madison Wisconsin. They checked the car over and found that Mercedes had rotated the tires, which you cannot do on an x5, I assume because of camber and whatnot. They said the two front tires were shot and charged me $800 for new tires. They also discovered that the engine was misfiring and going into limp mode because the coil packs were shot and I needed new ones. Those were covered under warranty luckily (they cost roughly $500)

I got the car back and noticed that my steering didn't feel as tight as it had before. I decided not to take it back in because I wanted to actually use the car which I was not yet able to do.

Two weeks later on the way into work I suddenly lose power and the car goes into limp mode the idrive says ENGINE MALFUNCTION, AWD MALFUNCTION, DSC MALFUNCTION, BRAKE MALFUNCTION. I pull over to the side of the road and turn the car off. I then turn the car back on and it runs perfectly. It runs just fine for the next week, then does the same thing again but this time dies in the middle of traffic. I shut the car off and turn it back on and everything is fine again. At this point I decide that it needs to go back into BMW so they figure out what the problem is.

I drop it off at BMW, their techs go over the car and decide that it is a faulty throttle wiring assembly. I am now just barely out of warranty, they charge me $450 for the wiring assembly and give me the car back. In the meantime I asked them to check the oil and oil filter, they only checked the oil level and nothing else.

I have the car back, I drive less then a mile and the service engine light comes on. I turn around and give it back to BMW. BMW says the check engine code is nothing (they never ran a test) they clear the code and give it back to me.

I start driving home and around twenty miles later I start hearing a horrible grinding and knocking noise coming from the engine. I put the car in park and shut it off. I call a towing company, because the car clearly should not be running and ask them to TOW it back to BMW in Madison which they do.

I tell the techs about what I heard and then I go home and wait for a call.

BMW calls me a few days later and says my engine is completely shot and that they found metal filings in my oil-filter. They also say that the oil filter is collapsed and that it is a cheap aftermarket oil filter and that it looks old. This confuses me since Mercedes was supposed to have put in a new oil filter less than 2,000 miles ago. BMW says a re-manufactured engine from BMW will cost me $25,000 and that labor will cost another $4,000. Add this to the $21,000 I paid less than three months ago and I am now driving around in a car that cost me $50,000 and is on its second engine at 70,000 miles. Needless to say I am displeased with the service I have received.

I go into BMW in Madison to complain. I feel that I have been ripped off by BMW because they did not look at the oil filter like I asked them too and they cleared a check engine code that might have been saying the engine was going to fail if something wasn't fixed.
BMW service manager claims that there is no way a check engine sensor could have predicted that the engine was going to fail. I ask him why no one test drove my vehicle and he claims it is my responsibility as the owner to test drive the vehicle, not theirs. I push him on the engine sensor issue and he says all the sensors are simply for emissions testing. They tell me I should ask Mercedes of Naperville to pay because I am so close to warranty and because I have had so many issues with the car. (Other minor issues, the passenger thigh support stopped working and the liftgate will no longer open)

I call Mercedes of Naperville and they claim that the oil filter is not the cause of this and that I am out of luck because they won't do anything. They claim that I should have purchased an extended warranty for an additional $5,000 for two years. They say that there is always danger when buying a used car and that it is not their responsibility.

I cannot afford $25,000 for a re manufactured engine. I just spent most of my money buying the car (I paid cash). I also cannot afford a used/salvage engine. BMW says that will cost me $15,000 to buy and put in. BMW says it will cost just as much to rebuild the engine.

Do you guys have any ideas for things I can try? I don't want to lose $21,000 on a car in less than three months.

Any help or information would be greatly appreciated.

(1974 Jaguar XJ12)
(1994 Jaguar xJ6)
(2005 Dodge Cummins)
(2012 Dodge Cummins)
(2008 BMW X5 4.8i)