I have had to replace one glow plug so far. 68,000 km on my truck. Failed about 15,000 kms ago, didnt impact anything except you could no longer use command start.
If you live in a colder environment, i strongly caution you against buying this truck UNLESS you are going to do the DEF delete. My truck needs a new def tank and there is zero in stock, zero in production and zero information on a potential date. Power has be derated and truck is basically rendered useless.
I am one extremely unhappy customer.