MTU 12V 2000 M94 Cylinder Head Gasket Failure

It just popped to my mind that I have a copy of it in my files.
It's specific for series 183 engines, which are different animals, but I'd expect MTU to follow the same approach throughout their range, on a topic like this. Below is the relevant abstract for the first service on new engines, and it doesn't mention heads retorque.

Elsewhere in the maintenance program, they do specify
"cylinder head: remove, check valve, valve guide, valve seat, valve steam"
but that's only for maintenance echelon "W5", which for 183 engines is every 3000 hours.

__________________________
MAINTENANCE TASK SCHEDULE:
· one-time operations after the FIRST 50 operating hours with a NEW ENGINE
· after W5 maintenance or after W6 major overhaul

1. attachments check tightness of securing screws and nuts
2. valve gear check valve clearance
3. fuel pre-filter clean /replace filter elements
4. fuel duplex filter replace filter elements
5. engine coolant pump check relief bore for obstruction
6. coolants pump check v-belt condition and tension
7. engine oil change
8. engine oil filter replace filter elements

Interesting failure, in that it's oil and not coolant. I have to wonder how there can be rust in the guide dowel area, but I'm more disposed to looking in the area of the lubrication system as the precursor of the oil leaks, something on the order of stuck pressure relief valve or a clogged gallery. Especially since there are no overheating episodes in memory despite head gasket failure allowing oil to leak on multiple cylinder heads.
I don't know specifically about these series of engines, but virtually all modern cylinder head assembly methods use angle-torquing or use torque-to-yield fasteners. These methods are a one shot approach at achieving maximum clamping force, and cannot be re-torqued, as the initial set point of torque before angle torquing cannot be regained, and in stretch-to-yield fasteners; they're a one use fastener. I would guess that these head bolts are a one-use fastener in the eyes of the manufacturer, but may spec a re-use criteria and you should certainly verify that the correct procedure is being followed.
Here is a link with some specs for the MTU-2000, which indicates that the procedure for setting head bolts is the angle-torquing method and that there is a maximum allowable elongation of the head bolts:
https://barringtondieselclub.co.za/mtu/mtu-2000.html

MTU 2000 Cylinder Head bolt torques
Max shaft length = 212 mm
Step 1 = 10 Nm
Step 2 = 50 Nm
Step 3 = 100 Nm
Step 4 = 200 Nm
Step 5 = +90 degrees, +10 degrees
Step 6 = +90 degrees, +10 degrees

I’ve seen a lot of it, I’m making the diagnosis by looking at the stain pattern on the head gasket. But willing to bet the deck of the block isn’t flat. Put a sheet of glass on it to check

I would agree with your conclusion on the possible alternatives.
Theoretically, the non-straight deck of the block that CJ suggested is a third possibility.
But it's hard to imagine that it took 800 hours to develop the leak, if that would be the reason.

Well, if it was I never heard of it, and I'd be genuinely interested to see some MAN tech doc mentioning it, if you can get hold of it.

BTW, the MTU schedule from which I made a cut and paste in post #21 is referred to their 183 engines.
And back in those days, both MAN and MTU used to marinize the very same blocks, sourced from Mercedes-Benz (who called them OM 400 series).
So, I couldn't think of any logical reason why they wouldn't have followed the same maintenance schedule, for non-marinized parts like the heads.
Then again, I can't be positive that they didn't...

How touchy. What you said just made me curious to understand better, nothing else.
If I would have thought that you were making that up, I wouldn't have even bothered asking.

Roger wilco.

Well, something went seriously wrong here. It's all localized to one side of the block and 3 joining cylinders. If you're sure of no overheating and not run WOT for a specific length of time. Sure the deck of the block is straight. It rules out a few things. Is the boat over-propped? Excessive exhaust back pressure, or exhaust gas temperatures on that bank? Bad turbo bypass and over-boost on that bank of cylinders?