Would a timing chain cover gasket leak cause oil to seep around the idler pulley, onto the belt, and cause a squeak? I've been trying to isolate this cold-engine squeal ever since I put on a 15% pulley on my 2005 MCS. It had about 25k miles when I put it on; I've driven 500 or so since then. I put in a new AC Delco 38404 tensioner with the pulley, and a Gates K060535 1379 mm belt, so that shouldn't be the source of the problem. I've been poking around with a mechanic's stethoscope, spraying water on he belt, and so on. The new belt I put on with the pulley looked glazed after only a few hundred miles, which is evidence of slipping I believe. I ran the engine briefly with the belt removed, and the sound disappeared. I put on a new belt, and the sound was much worse, but after a few minutes it went away. Then after driving a bit, it was back the same as before: squealing when cold, quieter when warmed up, but still noticeable inside the car above 2500 rpm. I removed the idler pulley to see if it was turning normally, and it seemed fine. Spun about as smoothly as the tensioner pulley does. But when I removed the pulley, I saw engine oil oozing out from the bolt hole. It was a droplet of about 1/4 teaspoon that flowed out when I removed the bolt. On the diagrams, there son'r appear to be any openings to the interior of the engine through that hole, but it does pass through the timing chain cover and the gasket appears, from the drawings, to be right next to that bolt hole. So is that the cause? Gasket starts to fail, oil comes up and around the bolt, drips past the spacer, and then runs down the sides of the pulley, causing the belt to slip?