Context is I have a 2002 c240, I know it's the bad one. Just did a serpentine belt and in less than 24 hours I have excessive wear on the front of the belt. I have an idler pulley in hand but I'm trying to identify any problems that can cause this kind of wear so quickly. Oil filter leak caused it to slip the first time, but we replaced this belt yesterday and the old belt doesn't show the same signs of wear.

any additional information would be nice to have.
ps. I know I'm an idiot eli5