Spin the idler pulley while you're at it. It's very inexpensive to replace and easy. But I believe I had to remove the fan because the bolt was too long (1999 ML 430) to remove from the idler.

Also wouldn't hurt to spin the tensioner for bearing noise. I replaced the belt and tensioner failed a few 100 miles later (granted, well over 120K on the tensioner so I'm not complaining).

I normally remove the fan assembly. From there, it's a few minute job to remove the old and put on a new belt.

You need the fan clutch wrenches to remove the fan assembly easily. I have an extra new unused one of the two that I need to put on ebay one of these day.

__________________
Jim