My friend has a 1996 Cadillac Seville SLS with the 4.6L Northstar. The car has about 125,000 miles on it. He doesn't know very much about cars, so while he is away at college, he doesn't do his own oil changes. Today he asked me if we could change the oil on the car because it was running really bad and it was quite low on oil. I knew it wasn't going to be pretty becuase his oil change ticket from Valvoline was from 12/18/02. I got under the car and noticed there was something written on the filter in permanent marker. It said "Inst. 9/22/02" and then it had two sets of initials on it. Well, 9/22/02 is the date of his previous oil change. It is VERY clear that they did not change the oil filter on 12/18/02 when they changed his oil. I don't understand how these "oil change" places can even be let to operate using such poor practices. Even if I didnt' have any arms or legs, I wouldn't let a quick lube place touch my car. Their quality of work is horrible. As I go to take the filter off... I quickly realized it wasn't tight whatsoever. I didn't even have to break it free. It just spun off with ZERO effort. Again... how can these oil change places get away with this? I would like to go back to this place and well... I dont want to get myself in trouble so i'll stop there. The oil came so black and dirty it was horrible. It had stuff in it and was SUPER thin. I put some Pennzoil 10w30 I had in it and a Supertech filter in it for now becuase I plan on changing it again in a month or so because I have a feeling it is quite messy in there. What damage could be done to the motor?