D-772 already torn apart

[bobcatmini]

I purchased a bobcat mt-52 mini loader with a kubota D-772 the machine was apparently smoking badly and the previous owner decided to take the head off. The third cylinder furthest from the radiator has black carbon buildup on top of the piston, it looks flaky, the other two cylinders look ok. The head gasket was intact. I know that a diesel blowing smoke can mean many things from air filter to fuel injector to piston rings worn.

Does anyone have experience with this engine, am I most likely looking at an engine with worn out rings, or is there some other likely cause(a fuel system problem?) that would create alot of carbon buildup on just one cylinder. The engine has 1300 hours on it.

Thanks for any help.
Andy