Here is a good one. A friend of mine went into a quickie oil change place and on the way home, at highway speed, noticed white smoke out the tail pipe. He went back and they replaced the drain plug that fell out, gave him new oil and 5 free oil changes as compensation. He was happy. A year later I told him he was blowing oil and he didn't know what I meant. To make a long story short the dealer rebuilt the motor from the crank bearings up, including a valve job (they thought that was the problem and did it first). The dealer would have left it with just the valve job but I made him take it back because it was still blowing oil. He was lucky because he had 3000 miles left on his extended warranty and drove the GM car to 150,000 miles. No one spoke of the oil change debacle but in my mind, it was the cause.
I love to change my own oil and get under the car to look around. I prefer to do my own work because no one cares about my car like I do. (That, and a tight wallet).
'85 500SL (Euro)