Steering wheel lock or key lock?
 

On my wifes 300sd she has a hard time starting the car. When she goes to turn the key it will not go to the right. You have to jiggle the steering wheel quite a bit until the key will go thru the detent. Is this fixable or just the nature of the beast. I tried and it did the same thing for me. Our other MBs do not have this problem.

DANGER,WARNING !
 

(It "Sounds Like" the Wheel Lock)

one of these past posts will clue you in:

http://www.peachparts.com/shopforum/tech-help/56742-steering-wheel-locked-ignition-will-not-turn.html?highlight=steering+lock+broken

And

http://www.peachparts.com/shopforum/diesel-discussion/281861-key-wont-turn-ignition-dreaded-bad-tumbler.html?highlight=steering+lock+broken

And

http://www.peachparts.com/shopforum/search.php?searchid=5487602

And

http://www.peachparts.com/shopforum/search.php?searchid=5487588

1.There's a possibility that your "Wheel Lock Bolt" is going south on you.
2.there's ALSO a possibility that your ignition switch "Lock Tumbler" is headed the same direction.
3. Maybe Both at Once?

Do Not Ignore these symptoms!

If the "Tumbler" locks up on you and you are unable to turn the key to the #2
position...YOU will have the devil's own time removing the "Tumbler" to replace it.
[I'd STOP driving the Chassis,until a New "Tumbler"
(and Mayhaps a New Steering Lock) are in hand for R+R !]

I've never heard of the Steering Locking Mechanism on a Mercedes "Locking"
whilst Driving...Due to Age and Wear...BUT if it did...Whoever's Driving is Mortician Bait on Wheels.

I've "Picked On" the 1985 SD for reference,since I've No Idea Your Chassis.

1. Remove key, turn upside down, insert and try again.
2. Try a spare key.

If 1 and 2 work, your key is worn.