Here ya go. This works for ignitions with the double sided key, Including 250sl's post vin# 2980. NOTE: this procedure will not work if you are unable to turn the key in your ignition. I suggest that anyone with a sticking tumbler take care of it now or you will be forever locked out of any attempt at repair and the entire ignition lock will need to be removed. Not a fun task.
First remove the outer aluminum escuchen by gently prying it off. The tabs behind will straighten out. (Photos 1 & 2)(Don't worry you can get it back in during reassembly by installing it before the lock cap and use a pick to bend the tabs back in place)
Next insert the key and turn to position 1. (photo 3)
Remove the key by slightly wiggling and pulling. This is detented so it takes a little more pull than usual. (photo 4)
Pull the chrome locking cap out. You can use a pick to get it started (photos 5 & 6))
With a pick, Depress the small detent pin on the left side of the ignition housing being sure to fully engage and hold it depressed. (Photos 7 & 8 )
With your spare hand, Grab the tumbler face with your finger nails or a second pick. (Photo 9)
Remove the tumbler. Notice the spring loaded detent pin on the left (Photo 10)
You can now disassemble, clean and inspect the tumbler and wafers by removing the snap ring. I suggest inserting the key during this to prevent everything from falling out. Installation is reverse of removal. ALWAYS reinstall the tumbler with it set to position 1 and do not disturb the inner housing cam. The aluminum escuchen should be reinstalled before the chrome locking cap so you can get behind it with a pick to bend the ears back in place.