There are no bushings that go through the sheet metal on that regulator. The bolt simply passes through the hole and the nut tightens against it. There is a rubber isolation mount that the bolt is pressed into, but it does not pass through the sheet metal. The nut is simply torqued down and holds the whole thing in place. Someone just didn't tighten that nut.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)