Howdy folks,
This is the nitty gritty on what is included in the MB repair kit.

ENGINES 601, 602, 603, 604, 605, 606, 611, 612, 613, 628, 646
REPAIR KIT FOR GLOW PLUG THREADS IN CYLINDER HEAD
A repair kit for damaged glow plug threads and/or broken off glow plugs in the cylinder head has been
developed. This repair kit allows for the drilling-out of the glow plug bore and the installation of threaded
inserts. As a result, the replacement of the cylinder head due to broken glow plugs (as an example) is no longer required.
The repair kit can be ordered as a Special Tool: 611 589 00 99 00.
In addition, the wear and tear components of the kit can be individually ordered as needed, along with
additional replacement threaded inserts.

Special Tool Glow Plug Repair Kit (complete kit) 611 589 00 99 00

The following replacement (wear and tear) items can be individually ordered:
Drill Bit, 8mm 611 589 00 99 03
Stop, 8mm Drill (used with 611 589 00 99 03) 611 589 00 99 04
Drill Bit, 5mm 611 589 00 99 07
Stop, 5mm Drill (used with 611 589 00 99 07) 611 589 00 99 08
Tap, M6 611 589 00 99 10
Stop, M6 Tap 611 589 00 99 11
Impact Adapter (M6 - M12) 611 589 00 99 13
Drill Bit, 3.5mm 611 589 00 99 15
Stop, 3.5mm Drill (used with 611 589 00 99 15) 611 589 00 99 16
Tap, M4 611 589 00 99 18
Stop, M4 Tap (used with 611 589 00 99 18) 611 589 00 99 19
Impact Adapter (M4 – M12) 611 589 00 99 21
Thread Cutter 611 589 00 99 22
Thread Awl 611 589 00 99 23
Thread Tap 611 589 00 99 24
Inserts, M10 (M10 x 1); (10 pcs.) 611 589 00 99 25
Wire Brush 611 589 00 99 27

The WIS document number for the detailed repair directions is
AR15.20-P-4112A for CDI engines.
So go grease up the palms of your local dealer's service manager or shop foreman, and thay can print these for you.

The glow plugs I have had to drill out or pull heads for have usually:
1. Melted, drooping into prechamber. Due to glow relay / afterglow failure.
2. Carbon, builds up around tip. Acts like cement. Most common.
3. Electrolosis. Happens with 606/611/648 glow plugs for some reason.

If your 210 diesel eats glow plugs, please make sure the afterglow feature
isn't sticking on. Check for 12v at glow plugs. Start car cold(<20 deg.)
Max on time for glow plugs after starting is 180 seconds. 12v should go away at 180sec or less. If not, like 5-10 minutes. You have failure of relay.

There is a tap/slide hammer adaptor for slide hammering out stuck plugs.
however, if the plug is melted into the pre-chamber. The head will need to
be removed so the center of the prechamber can be drilled out to access the mangled glow plug and cut/drill/blast out of head so the prechamber can be removed and head checked for damage.
Hope this helps a little.

Dr.Diesel