Mine was below the battery tray (you have to take it out, and was a rusted hole beside the drain. Filled it with expanding foam and treated the area with rust inhibitor and it's dry as a bone. Good luck

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Bob

03 ML320
99 C230K
85 300D 164K
93 190D 2.3 (sold)
62 220S (sold)
58 220S (sold twice -- a long story)