Good grief this sounds ominous!!

I am currently purchasing an OM606.910 with at least one inop glow plug. [no light until afterglow]
What type and size of socket removes the intake manifold? [need to go ahead and get stuff together]
What exactly breaks on these glowplugs? The tip breaks off inside the head, it snaps at the threads? What??? With all the back and forth stuff it sounds like maybe the tip is the issue?
Diesel911, do you have any of these glow plug reamers available? I've loaned out the OM616/617 reamer twice that I got from you, but have yet to use it. I now need one for an OM606......