Cat D4C steering clutches

Hello everyone, I'm having a problem with my employer. I have a D4C that was sold and the customer is complaining that the right side is not working. First thing I did was move it outside and bury the blade into the ground and the right side will not drive. The brake band adjustment is tightened fully – there's no more adjustment to it – and the pedal still goes all the way to the firewall. I am telling the owner that the clutches are out but he's telling me that there's something wrong with the brake.The left side drives just fine. After burying the blade I can step on the right brake and the left side just digs into the ground and has plenty of pull to it. When I step on the left brake nothing happens on the right side, full throttle first gear right side does nothing and I cannot convince him that it is the clutches. He didn't like what I told him so he called an independent mechanic who has been working on these things for years and that mechanic told him that it was the clutches so he called another mechanic and that mechanic told him it was the clutches so he called his son who has been in the business for many years and his son told him it is the clutches but he will not believe any of us. At first he told me it's the steering valves, he had me rebuild both steering valves, and now he's telling me it's the brake and he says I guarantee it's the brake. Is there something else that can cause the right side to not drive? There's plenty of oil in the clutches and all of the linkages are adjusted properly and I don't know what else to do. Somebody please help me!