I installed new injectors in my '91 300SE a few years back. Very straight-forward repair, no priming or anything required at all. just bolt them in and go.
I had a very slight stumble at warm idle, and sometimes it would chug for a few seconds at warm or cool startup. Both problems pretty much went away.
Now, after another 50k miles or so, I am noticing the same symptoms.
back then I paid $21 each, now over $30 is best I can find.
Saw an add in eBay, a guy in England sells them, if you're gutsy.
still, $36 each ain't so bad every 10-15 years or so.

Oh, this chugging at start-up has me kinda thinking it's not just the injectors.
doesn't do it cold, just when warm, or kinda warm, when the idle speed isn't increased. if you give it some throttle it kinda clears it's throat, and seems to fire 3, then 4 then 5, then 6, and all is smooth. Could it be the fuel metering thingy?

DG