This 56 Viking is equipped with a pair of 1550 MAN Classic common rail engines. The captain reported coolant loss and steam present from the exhaust on the port engine while underway. Before starting any work in the engine room, a plastic wrap was laid to protect the raw teak timber deck and points of access. Inspecting a cylinder with the boroscope showed a clear view of a section of a valve seat. Upon further inspection with the boroscope, a coolant trail could be clearly seen on the cylinder liner. We found that the top liner O-ring had failed, and all pistons and liners were removed. The engine was rebuilt with all genuine parts. It is worth noting that when using a MAN Authorized dealer, all genuine parts and labor come with a 2-year warranty. A full power sea trial was completed to confirm operation, and finally, the paint was touched up before returning her to the customer.