Best way to clean injectors?

I can't comment on the diagnostics side. But, I have done a purge this last weekend and did one about 15000 miles ago. It definitely made a big difference to engine noise and smoothness. There are some good guides out there too. It's relatively cheap place to start.

I did a fuel filter change afterwards and poured the last bit into the new filter and topped it up with diesel before reconnecting the pipes. I did a purge because I was getting a hesitation and what felt like a misfire sporadically.

Not sure if it helps you.