About 6 months ago I sold my mom's mint 2008 CTS to a female friend at work. As part of the deal, I gave her the next 4 oil changes free. I figure the car going to a "good home" and I would ensure it was maintained with the proper oil and kept up. Well, since she had it she had 2 accidents, but the car was fixed perfectly. This last time they did an oil change for her....even though the OLM was still at 65% essentially dumping perfectly good Mobil 1 EP for who knows what oil they used. HERE IS THE CLINCHER: She came by the house today to drop off some stuff and have me check the bosyshop's repair work. I go out to give my usual courtesy oil check and NO OIL at all on the stick. I show her and remind her that I told her she needs to check the oil! That is when she said she just had it changed. I added 3.5 qts of oil. Figured we were good. Nope - she pulls away and oil trailing under the car! I stopped her and showed her the oil and immediately put it up on my lift. Drain plug was tight - the oil was coming out of the oil filter adapter and down the engine, filled up the belly pan and the whole entire underbody was wet with oil all the way to the rear bumper!! ROOT CAUSE: the person changing the oil filter had the o-ring on the cap threads and NOT on the recess groove where it is supposed to be, the oil flowed thru the threads and out the cap. Therefore the woman, had she not came to my house and I checked the oil, would have burned up that engine today!