Had an oil change at the local express lube on my

Had an oil change at the local express lube on my 2002 Hyundai and have been doing so for years. Noticed that the lifters were noisy (sounded like a dodge slant 6). I figured it was my imagination and it has been doing it for a while, just didn't notice. Then it was getting louder. So about 500 miles after the oil change, I checked the dipstick. no oil. I called the oil shop and told them that the engine had no oil. The manager came down and added 3 quarts before it was measuring on the dip stick. I brought the car down later that day and they added another quart. The engine holds 4.5 quarts. The manager looked all around the underside of the car/engine looking for signs of a leak, 4 quarts worth in 500 miles. No leaks. They asked me to bring the car back in 500 miles, and I did. The dipstick still measured full.
So what's in this for me? I ran my engine will little to no oil, and there has to be damage. I have all the conversations recorded to protect me from the 'I don't know what you are talking about sir, we never make a mistake.' What type of damages should I be asking the owner for? 1/2 the cost to replace the engine? I am not looking for a new car, but I certainly have damages that should be compensated for.