W123 OM617 missing on a cylinder. Test injectors?

[whyameye]

I have a 1985 W123 which first developed a rough idle and now seems to be sporadically "missing" on one cylinder at all RPM. I've had clogged fuel filters before and the symptoms seem different. I thought the next thing to check might be the injectors and I'm looking for a simple way to test to see if one in particular is bad. I'm finding lots of instructions about replacing all of the injectors or cleaning all of the injectors or building a "pop" tester but I'd like to start with something simple and fast. I see lots of people talking about about "cracking a line" but I've burned out Google trying to get the specifics of what that literally and specifically means. I'm guessing I open the line for each injector (where, exactly in the line, though) and see if the idle gets worse or not? If it doesn't get worse, that's the bad injector? Anybody have a link or tips for me?