I second on the other replies. I read somewhere in the forum that you really shouldn't try to lubricate the ignition lock.
Do a search as you will find materials for the whole replacement on the forum. I had the same problem put endid up vibrating my key to get it turned. Do the removal a.s.a.p and get a borrowed tumbler from your local dealer.
In my case I just replaced the tumbler although my dealer suggested to change both tumbler and steering lock mechanics. Now it works fine and there haven't been any problem with the lock.
My topic on this was: Ignition lock broken - help needed.
'87 MBenz 190E 2,3 8vlv