No expert, but if your getting a Running Rich code, signs for a internally leaking injector would be hard cold start (taking longer than 2+ seconds), carbon soot at tail pipe, <10% reduction in fuel mileage, slightly rough at idle but no noticable problems at WideOpen, and the loss of fuel pressure after the engine is turned off.
A scan tool could verify that engine sensors (MAP, ECT, MAF, EGR, etc)are working properly and that the main computer (PCM) is trying to reduce the fuel delivered. As most systems can only increase or decrease deliver by ~15%, it will give some identication that it can't control the situation.
There's no code (OBD I or II) for a leaky injector; most newer vehicles (OBD II) would get a P0172 (System Rich) code and eventually if ignored a P0420 (catalyst effectiveness low).
From working on fuel inj'ed vehicles for 10 years now, I can say that as regular maintenance, injector cleaner should be added to a tank of fuel every other oil change or so, but its unlikely that cleaner will help in your situation, deposit are either causing one injector not to flow enough so vechile is increasing output of all injector (weakest link) to compensate/ protect for a more dangerously lean condition.
Averaging around $100 for one injector for local parts store, I suggest repalcing all as a set (assuming that the current set is original equipment). Ouch! But if you could test the fuel pressure (see earlier) but with the injectors attached to the fuel rail but out of the engine, you could find the culprit singularly.