Jon,
I DON'T believe this is an adjustment problem, I also DON'T believe it is a lubrication problem!
I looked at the valves ONLY as a PM. By doing this you get the only chance to take a look at things, I by no way am recommending that you tear down the motor just for the fun of it.
It is my opinion that Detroit Diesel has a problem with this area of the motor, like I said earlier, 2 for 2. I also have no idea how long the motor would have run before the cam would wear enough to effect the operation of the motor. I just feel better knowing this was done and I will do it again at 220,000 miles, God willing the economy holds up and I still have this bus!