So a while back, 7-8 years ago, I worked in a quick lube local to St. Louis. I was an oil tech and a man pulled in a new to him rental truck, it was a Dodge Ram I believe but specifically it had a topside cartridge filter. Now I’d worked there for about 3 years and had many a car come in that was neglected on maintenance but this truck I’ll never forget. I pull it in and start going through the motions, get the mileage and go about raising the truck. I crack the drain plug and as soon as the oil began to drain I new something was wrong, enough so I called another tech over to check out the thickness and darkness of the oil. I put the plug back in lower the truck and go to remove the cartridge filter, it was extremely tight, more so than one that was over tightened and required me to get a few extra hands to break it loose. What I pulled out of the depths of that filter housing was pretty well unbelievable, the filter had become something ungodly full of sludge and thick black almost a hard, chunky tar. I immediately got my service manager to show him something was terribly wrong and after retrieving the oil change reminder from the window did we realize the oil change was something around 30-35k miles over due and we believe it would have been it’s second oil change since it only had around 40k on it. Customer was oddly enough pissed at me because somehow I caused this but yea long story short easily top 5 craziest things I seen while working there.