Most M.A.N.s are high performance engines. 1300s are compound turbocharged, with intercooling and aftercooling. Every component in them is highly stressed. I have turbochargers sitting here that are perfectly good except the exhaust housings are cracked from thermal stress. Even though they'll function just fine right now they're ticking time bombs.
While we don't usually get reports on service history of injectors it's not hard to believe that injector nozzles stuffed into cylinders that are seeing the kinds of temps that crack exhaust housings like that wouldn't last long either. They're subject to high opening pressures combined and high cylinder temperatures which combines to beat the life out of them. We hear rumors circulating that brand X nozzles eliminate smoking on M.A.N.s but the problems are also eliminated when we put a set of OE nozzles in them. The real problem is that they're just shot.
I'd doubt the valves or the pistons have an easier life.
This goes to the HP/cu. in. rule. Engines like that are for people with unlimited funding. Or to paraphrase Mad Max, "Speed is just a question of money. How fast can you afford to go?"
Also, 30K hours on any injectors, lightly loaded or not seems like a lot. They may spray and the cylinders may fire, but I'd doubt they're doing the combustion process, or engine life and efficiency any favors.