You are right on the money with that one. Trouble free driving doesn't mean that you never open the hood and the tool box, it just means that you're doing preventive maintenance not corrective maintenance. BTW I'm not totally down on Chevy's. I have an '88 stick shift Vette.
The seals at the injectors will not cause the trouble you describe, they will cause a rough idle due to a vacuum leak. The previous poster made a very good point about a bad injector. These injectors will stick, when they do, they're through, cleaning agents will not unstick them.
You need to first use a noid light at each injector to ensure that they are all getting a signal. Then you can find the offending injector by removing the injector connectors one at a time until you find the one that does not effect the idle, much like we did with plug wires before the days of electronic ignitions. I have done this before to find an injector that was stuck closed. I'm not sure this will find one that is sticking open when shut down.
Best of luck,