I have a pair of the Yanmar 6cxgte2 with about 1600 hours. I am not having any issues but I am wondering when I should pull the injectors to have them checked.
Yanmars, you should have done them already (if memory serves me right) and adjusted the valves. I would do them when the Yanmar maintenance interval says to do them. If you don't, they might be stuck in the head and you might be pulling the head to change injectors in a worst case scenario.
I have had the valves done last winter, but have not pulled the injectors for the "pop" test. Guessing it is time to do so.
Not to be flippant, but when all else fails read the instructions. There is a service manual that goes with ANY engine and there is a lot more than oil changes and injectors in there. A rebuilt engine is well into 5 figures, plus the substantial cost of R&R, not to mention the hassle. Following the maintenance schedule on all components will postpone the inevitable as long as possible. Unless you got money to spare and then it doesn't matter.