Just tried starting 83 mb key won't turn
 

Key won't turn in ignition on 83 MB. Is this a major catsastrophy?? Any suggestions I might try etc.?

You've got to use every possible capability to get it to turn one last time to the #1 position. Use a vibrating sander...........play with the key........use some lock lubricant...........but, get it to turn one last time and don't turn it back.

The tumbler is shot and you'll need a replacement from the dealer.

If you can't get it to turn, you'll have to spend considerable money to replace the entire ignition lock assembly............a long and tedious process..........or a very costly one.

Pull the key out about 1 or 2mm and try to turn it, if you get it to turn do not turn it back. Leave it in the 1st or 2nd position and disconnect the battery so it does run dry. Then just replace the tubler following the instructions on dieselgiant.com

What are the chances its only the tumbler? Which a new one from the dealer will cure, as opposed to the actual "bolt" mechanism? Got my fingers crossed for him.

Try blowing powdered graphite lube into the slot then jiggling it. Don't use the kind in a spray can. That has oil in it that will make matters worse...use the dry kind in a little tube from any auto parts store.

It is kinda messy -- pencil colored dust goes all over the console, but alot less messy than grinding out the whole key mechanism!

Could it be only the steering lock? Try to move the steering wheel back and forth a bit while you turn the key. Maybe it will unlock and work.

It may be either the tumbler or the steering wheel lock - you can't tell simply because the key won't unlock the ignition. If it's the tumbler it's easy to replace and is available from your local MB dealer for about $80 and includes a new key - you have to prove ownership and have your VIN number for them to order it - and all your locks will still work from a single key.
However, it may be the steering wheel lock.
Either way, one way to free the key is to jack up one side of your front end and have someone turn the road wheel forward and back to jiggle the lock assembly while you jiggle the key to try to free it - it's much better leverage against the steering lock that trying to whip your steering wheel back and forth.
If it's the steering lock, you can drive it as long as you need to, so long as you cut your wheels fully right or left before you shut off the ignition when you park the car - the steering wheel lock will not engage if the wheels are way off of dead center.

99% sure it's the tumbler. You want to get that key to turn or it will be an expensive proposition. Spray some WD40 in the key slot then start wiggling the key. It took me 45 minutes to get mine to turn. It was well worth it though.

Once the key is turned LEAVE IT TURNED. You can then search for tumbler extraction instructions which is a pretty simple process. Once the tumbler is out you can start the car using a flat head screw driver. I went a year doing that and telling people that the valet key was a phillips head.;) Good luck and let us know how you make out.

that has happened to me and my car 4 times, all i do is get the spare key, spray wd40 and get the attachment tip on there and spray in there then get pliers on the spare key and then gently give force, my idea is if you get it unstuck keep it lubed up, the last this happened to me was 4 months ago and its turning smooth.

some advice is to get a brand new cut key from your mercedes benz dealer ship, i got a new one and i was shocked... how does the key turn haha, it was so worn out.