This reads like the second shop is in agreement with the KW shop. I don't see a case against the KW shop. At least not one that you would win.
No Moot, Kenworth is saying that it was an injector that caused the meltdown. I have talked to six different well know service managers from Cummins, Freightliner, and Kenworth. I send them pictures of the engine and I was told this happens from lack of oil. I was told the same thing from five different people that don't know each other. It is common that the number six cylinder will do this from lack of oil. I hope Kenworth Corp does the right thing on this, time will tell.