I have an'06 3500 with 200k miles. fuel injectors 1,2,4,5 are stuck. We were able to remove #1 with the tool we bought online and a 50lb slide hammer (took a while). The Sprinter will run, is there anything I can add to the fuel that will help loosen the other injectors? What is the best additive I can add to the diesel fuel going forward? thanks.