On the Buy Parts page, it has two choices for engine number range for the belt tensioner spring:
-10-030482
-12-019162
It's just above freezing in my garage, so my enthusiasm for cleaning off the engine and searching for the number is not too great, but I need to get the part ordered. It was cold enough that I was zable to drive 5 miles home without overheating with the belt slipping though.

Reid

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Reid
Past ('59 220Sb, 2-'59 190's, '92 300D 2.5T)
Current
'04 E320 4Matic Wagon
'00 E320 4Matic Wagon