Here the first page from the catalogue "MTU Diesel Engines 16V 4000 M53/M63 for Vessels with Unrestricted Continuous Operation (1A)", which returns results for: reduction gearbox
Here the first page from the catalogue "MTU Diesel engines 12V 4000 M53/M63 for Vessels with Unrestricted Continuous Operation (1A)", which returns results for: reduction gearbox