Nissan Navara STX injector leakage

My 2008 Nissan Navara STX needed injectors at 70,000 km and they were replaced under warranty. They needed replacing again at 104,000 km, but this time Nissan wanted the injectors sent to an independent company to be assessed. It was found that three injectors had excessive leakage, and all needed to be replaced. Nissan offered to pay for half the price of the injectors, which was $1354.64. That left me to pay the remainder, including the independent testing, which amounted to $2500. I think this is unfair and I am pursuing Nissan for the full payment. Are injector faults common with Nissan?