A 1.5mm hex key (allen wrench) works well for inserting into the hole, and is rigid enough to work well. There is a steering lock removal tool (about $20) that is made to facilitate the unscrewing of the cover with no scratching--and makes the job much easier than trying to use large needle nosed pliers to get a grip on the cover. One of those rarely used tools that is great to have once every two or three years.

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Earl McLain
'02 C230 Kompressor
'89 560 SEL "Frau BlueCar" (retired April 2004)