We were traveling in Eastern Washington a few years ago on a Sunday PM. Talk about the middle of nowhere. We were driving our '87 300E with 128K. A noise started abd got worse. I stopped next to a wheat field and thought it was the fan clutch. Wenatchee was still 65 miles away. I figured that if it let loose I would lose the clutch and maybe the radiator. To make a long story short, we limped into Wenatchee late after noon, got a motel and found a good repair shop (called the local Big Three service managers and asked them for a Mercedes recommendation)
It turned out to be the idler pulley for the belt system. I would do a preemptive strike and change it before you leave, since it also happened to a 190E that i had with about the same mileage.
Anziani
'95 E420 90K
'87 300E 175K