Little tip I've learned with allen bolts on these cars.......some #000 steel wool is your friend. Tear off a tiny pad and stretch it out, lay it over the recess in the allen screw, force the bit in. It won't strip, it won't slip, and it'll hold the screw on the allen key when you reinstall it.

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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!)