MAN V10 - 1050hp LE403s

Hey, why don't you read what I wrote, rather than making it up on my behalf?

YOU are reiterating to boredom that your engines are smooth, while it's widely known (no matter how happy you can be about them, which I never argued against!) that V12s are smoother.
In fact, the behaviour that motoryachtlover describes is in my experience completely normal.

YOU used the expression "The cutout actually closes the injectors", which is misleading because it's perfectly possible, but only with electronic injectors, which do not require any sort of "spigot off", to use your own wording.

Last but not least, I literally said "I'm not insisting" on the cutout feature. What else are you expecting me to say, in order to reciprocate?!?

Bosch injectors/nozzles are indeed crucial in these engines.
Not because they aren't reliable - it's actually the opposite, in general: they are less sensitive to dirt or watered fuel, when compared to more modern, higher pressure injectors.
But if and when they leak, in the worst case they can lead to severe piston damage.
So, I think you did the right thing pulling also all the others.
Replacing them is almost unheard of, though: normally, any good Bosch service can refurbish them, i.e. replace the nozzles, tune opening pressure, and they are as good as new for at least another thousand of hours.
Of course, during such check, they also verify if any replacement is necessary, but I'm aware of a boat with 4k hours on her V12s (whose injectors are the same as in V10 and V8), and none of them have ever been replaced.

Ref. idle RPM, I'd suggest to use a laser tachometer to check it, because the accuracy of VDO analogue gauges usually mated to these engines leaves something to be desired.
It's only 20 bucks or so, and dead easy to use: you stick a piece of reflective tape on the belt pulley, and you're good to go.
Btw, that's also useful to sync the engines exactly at cruising speed, cross-checking what the instruments show.
In my boat, I cruise mostly at 1800 rpm, but after checking with the laser tacho I found that I'm perfectly in sync when the needle is a hair above in one engine and a hair below in the other.

Do you mean permanently wired?
If so, I'd be curious to hear more about them, because the original engine control box designed for e/r installatiom (which was a MAN option), aside from start/stop and a few basic instruments, featured the very same analogue VDO tach which was normally fitted in the dashboard.

More than just heard, I've actually seen a holed piston due to that.
But I'm not sure if that had anything to see with the brand.
Actually, I wasn't even aware that MAN ever used anything else than Bosch, are you sure that they also fitted Monarchs?

Anyway, as I was told, this doesn't happen out of the blue, but it's rather due to progressive oxidation/degradation, possibly due to lack of use, rather than excessive.
The two tips I was given, and which I included in my routine checks, are as follows:
1) upon cold start, particularly after the engines stayed unused for some time, look for spots of fuel floating on the surface near the exhaust ports. There should be none at all, normally;
2) once warmed up, smoke at idle and low rpm should be low, and comparable in both engines.

FWIW, I refurbished the injector (new nozzles and pressure check/adjust) on my boat at almost 1500 hours, not because of any particular problem but just as preventative maintenance.
None of them was too far from rated pressure, just generally a bit lower, by somewhere between 10 and 20 bar at worst.
No leaks, but the nozzle spray wasn't as regular as it's supposed to be.
Since that job, I didn't see any meaningful performance improvement, but I did notice much less soot on the hull sides (almost none, in fact), around the exhaust bypass.
Which gave me some confidence to not have thrown money away for nothing...

Sounds interesting, thanks in advance for confirming the brand/model!

Great, many thanks.
As I understood from Aetna website, I guess the instrument must be feeded by their 8901 senders, installed somewhere on the engine.
If the next time you'll be onboard you would have a chance to check where the sender goes, I would appreciate!

Well, considering the multiple sources, that's more than likely correct, I suppose.
Sorry to have relayed a wrong indication, regardless of how reliable my source was - or should have been, theoretically...