Manufacturers of engines seem to always warn against additives, irrespective of changes in fuel quality because they can't control what you may introduce to your equipment. Besides, they love to void their warranty exposure whenever possible. Low sulfur diesel is bad for engines. Unleaded gas with ethanol is destructive to small engines, yet garden tractors/mowers, etc all warn against using lead additives or alternative fuels (I use leaded gas). The local small engine repair shop recommended it.
The "shade-tree mechanic" I use has kept cars and trucks and farm equipment running in this agriculture community for over forty years. He knows what current fuels do to engines. If he uses ATF in his personal vehicle, I'll call that good.
My question had more to do with diesel engines operating in a marine environment. These old marinized tractor engines, like i have, weren't designed to operate on low-sulfur, low lubricity fuels. Maybe the new diesels are.
The only "additive" system I know of on a diesel here in the states is the DEF where ionized water and urea are sprayed into the exhaust system to cut down on pollution. Owners hate it...just another system to have to monitor.