05 E320 CDI - stuck, but not broken, glow plug
 

Any recommendations on how to remove a glow plug that's been unscrewed and is free of the threads but won't pull out of the hole, presumably due to carbon build-up?

You can buy or make a split nut that is assembled on the thread portion and held by a wrench to allow you to unscrew it a bit farther. If you can grip it with a slide hammer that should also work.

Be careful, the direct injected glow plugs have ceramic tips not steel like the older ones…

http://www.peachparts.com/shopforum/diesel-discussion/351809-gregmns-1991-w126-350sdl-has-new-home.html

Read post #15

Thanks, GregMN. I wasn't sure what the split nut nelbur referred to was, now I know!

Find some way to get Kroil. PB Blaster or some lesser penatrating oil into what space there is around the threads. The object is to try to let is seep into the carbon that has it trapped and possibly dissolve some of it our lube it.
I don't know if it it is possible to create sort of a bowel (with epoxy putty) around the glow plug so that you can fill it up with a pool of penetrating oil. I think that would get a larger amount of the oil inside where it is needed.

Once out sounds like you need a glow plug reamer or some other method to clean the carbon out of the hole.