How does he come up with "weak injectors". All of them?? If you are burning oil, check the plugs. If they are oil fouled, that is your problem. depending on what they did when the head gasket was done, you may be looking at valve seals or possibly valve guides as well.
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.