There's no "inventing" the tool.

It's a tamper-resistant Torx-Plus and you can get one from Mercedes.

If you have the Mercedes W211 Service DVD all required procedures are included, and the special tools required are listed by part number. From your dealer or at 800.for.merc

IIRC the cover can be removed without removing the internals from the door. Certainly the glass can be. Don't tear up the screws until you verify this.

Replacement prepainted mirror covers are available from Mercedes

You can reuse the mirror and turn sig led unit.

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Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles