Well, I have this strange CRD I got from a lost member a few years back. It finally made its way to the front of the inventory, and it ran like one or 2 cylinders were dead. I pulled the cover to find all 4 rockers on #2 snapped. I figured failed rod bolts like I've seen before, so I pulled the head to confirm, and the cylinder looks great, so do the valves.
The only thing I can think of is that maybe they knocked off a rocker or two when they reassembled it, that maybe the pressure eventually snapped the others. Wouldn't the intake valves have tremendous pressure placed on them if the exhaust valves failed to open?
The last test I can think of is to turn it over with the head off to listen for knocking, but the carbon ring at the top of that cylinder shows me that the piston hasn't been rising too far upwards. Hmm, I'd appreciate any ideas before I go and throw the head back on with new exhaust valves (200k miles), -and cross my fingers that it's not a huge waste of time...