On these common rail diesels, it's pretty common for these injectors to have a lifespan of just over 100k miles. They've all been subjected to the same miles and suffered the same wear over their lives. At this point, I don't think I'd replace just one and risk having another fail in a matter of weeks, especially if it might melt a piston and trash my engine. I would personally find the best deal from a REPUTABLE store and replace them on my own to mitigate the expense as best as I could. I understand that many people may not be willing to do that.