| Let me try to clear up some things on the injector bulletin/extended warranty. I will first say that I do not 100% agree with it but this is the way GM wants it.
First of all this is not a recall so the dealers are not supposed to replace the injectors unless they are bad.
The second part is where it gets interesting. The special policy states that only the failures noted in the bulletin are covered for the extended warranty period. Which means, as stated in the special policy, injector body cracks and high pressure seal extrusion. These are the problems that caused the injectors to leak fuel into the engine oil. A seal would leak or the body would crack and fuel would spray out from underneath the top cap of the injector. This problem has been resolved with all replacement sets of injectors. The other problem is ball seat erosion. This is the problem that causes high return rate. High return rate is where the injectors return to much fuel back the return line. So much fuel that the injection pump can not build enough fuel pressure and will set the notorious P1093 P0093 codes. The bulletin states only these failures are covered which are identified by high return rates. The dealer is supposed to measure how much fuel all 4 injectors on the left bank is returning and how much fuel all 4 injectors on the right bank are returning. We hook into the return lines and crank the engine over for 15 seconds and measure the amount of diesel fuel comming out. If it is above the spec that GM gives us then all 8 injectors are to be replaced. Another note is that balancing rates will not in any way reflect the return rate of an injector. The ECM adjusts balancing rates to obtain a smooth idle. A very high or very low balancing rate does indicate an injector problem. A high balancing rate could also indicate low comprssion in a cylinder, but that is less likely. It is usually the injector at fault.
So all this being said, injectors that have other problems like smoke at idle, high balancing rate, and misfire, are technically not covered under this specially policy. Injectors with these failures are only covered under the 5year 100,000 mile warrany and are supposed to be fix as failed meaning only replace the one or ones that are bad! I, like jaydawg, do not like to put in just one injector in a lb7 because they will generally come back within 6 months needing another injector.
I do not believe that rust in the fuel filter is grounds for voiding the warrenty. The fuel filter should pick up these particles. Further more I believe the rust in the fuel filter comes from the inside of the fuel lines rusting. I believe this is caused by excessive use of diesel fuel additives-mostly diesel fuel cleaners. The cleaners tend to remove the coating from the inside of the fuel lines and they rust. This rust can also prevent the hand primer from working by getting trapped under one of the check valves inside the hand primer. The only additive I would recommend is a lubricity additive unless you have an injector problem you think can be fixed with a cleaner.
This should help explain why some dealers say the injectors are not covered in some instances like smoke because it does not have high return rate. Some dealers have been charged the price of the injectors back by GM for replacing injectors that do not have high return rate. Yes thats about $3200 at warranty cost. So some dealers are trying to follow the bulletin to the "T" so this will not happen to them or happen again.
I hope this clears up some of the inconsistency that we see on this forum often regarding the replacement of lb7 injectors. Like I said I do not completly agree with it but that is the way the bulletin reads!!! | 
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