My engine was throwing some check engine codes stating a few issues with the glow plugs and controller. Since I didn't know the history of them I decided to go ahead and replace them. The glow plug light was taking a while to turn on also so went ahead and did it. (Here is a good write up from Sprinter-Source)
Parts:
Also you can get a kit with everything from Europarts-SD too.
Tools:
After doing a lot of research I was really concerned with breaking off one of the spark plugs. To prevent that I used a lot of PB Blaster and performed the removal when the engine was warm.
So PB Blast them for a long time beforehand and then after warming up the engine use the hose pliers to remove the electrical connectors and then the 10mm deep socket (sometimes with a swivel adapter) to slowly remove the glow plugs. If it starts to get hard to turn them, tighten them in slightly, spray PB Blaster and try again. DO NOT FORCE THEM! It is a big problem if then snap off and get stuck in the head.
I got luck enough that they removed easily and no issues. Installing them is just the reverse. Do not over-tighten, they are only 10mm and a lot smaller than spark plugs.
The glow plug controller is an easy swap out behind the driver side headlight assembly, the headlight wire harness are a pain to remove so I just set the headlight aside while I performed the replacement.
I recommend while you are in there you check all connections for corrosion and remove any corrosion (I use this on a drill to remove corrosion) and then add dielectric grease to prevent future corrosion.
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