I considered two vessels for purchase that had the NT855s. Some have dry exhaust manifolds with soot leakage that really makes a mess of things and clogs air filters. Largely irreparable too as the engines were designed for truck and equipment use where minor leakage is not an issue. Tony Athens is quire familiar with these engines and this issue. Communicate with him as you're in SoCal.
A white glove inspection will reveal the extent of problems, if any.