Has anyone had this problem? Lots of Sprinter owners! The glow plug failures are so common that some are looking at them as disposable wear items. I have a failed #6 right now, with parts on the way. #6, driver side rear, is the one I hear about most often.
Bad diesel? Probably not, but not enough info to really know.
What would it take to fix? A new glow plug, obviously. A Bosch replacement can be had for $20. From the dealer about $50. Even though it is usually a quick and easy job, I've heard of ~$200 for labor because they are sometimes seized in the head with a risk of breaking off. The driver side glow plugs are more difficult to get to because of turbocharger plumbing. Some owners have them all replaced when one goes out. I just read a report of $700 for all 6 at a Mercedes dealer, including a new control module. I'm a little perplexed by the control module part. While in the Sprinter I5 a shorted plug would also take out the control module, I though that situation was fixed with the V6. Maybe not?
DO NOT go without replacing the glow plug. Even though the engine will start and run fine, DPF regeneration will not take place. A clogged DPF can cost really big bucks. If you're tempted to do the job yourself, I suggest you spend time reading about in on the Sprinter Forum.