It sounds like he has more of a problem with the distributer. The l10s, M11s, and N14s have all been great for us. Most areas of the country have private guys that know this design of engine well and may be an option someday if a guy has trouble. I have found Cummins to be no more trouble than any other brand of engine. When it comes time you need help it can hurt no matter what brand you have. Keep the oil fresh and above the add mark, coolant fresh and conditioned, coolant temp within operating range, warmed up and cooled down properly, and tuned up within reasonable time or when running rough and you'll be good to go with most any brand. If any of the above has been violated over the life of the engine a problem could be under way. logged errors in engine controlers could tip a guy off on some misuse practices.