Not to be contrary, but if the wheel has not ever been removed, or if it has and replaced per factory spec, it will have red thread locker on it. The bolt is "micro encapsulated", to use MB-Speak. Brute force has worked for folk in the past, but why risk it?

Judicious application of heat melts the thread locker, and the bolt removes with less force...

Excellent advice about the key and scotching the wheel... Some have turned the wheel fully to the left and let steering geometry hold, while others have used wood props and pipe, as reported in this thread. Regardless, DO NOT RELY ON THE STEERING COLUMN LOCK!

__________________
RM Smith
1988 560SL

"Where is it again that we are going, and why are we in this handbasket"?