Diesel injector testing/cleaning
 

I have purchased a Zeca injector tester to check my 240D injectors.
I have a popping sound on one cylinder, with a rough idle. The last time this happened I put in four Bosch reman injectors and it fixed it. But this time I want to only replace the bad one(s).

The test stand instructions recommend using a Shell calibration fluid, not Diesel fuel. Is it worth looking around for this cal. fluid? I was under the impression that shops used fuel to test injectors.
US Diesel, who sold me the test stand, said Diesel is not recommended because of fire hazard. How much of a hazard is it?

Also, when I find the malfunctioning injector, is it worth cleaning it, or should I just buy a Bosch reman injector? If I'm going to clean it, I need to find a Bosch needle of a specific diameter to clean out the orifices, according to the factory service manual.

Thanks in advance for any advice you can provide.