Well, I have done over 1500 miles on the car without issues. Temperature is under 110C even in the hottest days going uphill. It stays between 85 to 100C most of the time during city traffic or on freeway. Not losing a single drop of coolant, top radiator hose is soft to touch in the morning. So I cannot complain. The nightmare scenario as predicted did not come to pass. I took pictures of the valves before I installed the head. Cracks were there but they are all surface cracks. So cracks do not mean the head is doomed. You need to pressure test it. I make do it myself and it came out OK. This is NOT luck that the head works out OK, I mitigate my risk. Will report back in 10K miles.

btw: the head has a lot of surface scratches. Some are quite deep as you can see from the picture. I did not plane it down. I sprayed Permatex copper spray on the head gasket and it works out great so far.

Most of the cracks are larger than I'd be comfortable with letting go but all in the name of science !

The type of crack that is generally OK to let go is in pic 3 , bottom , between the valves.

The next questions are:

Has anyone pressure checked a head, found one that was actually leaking and documented the cracks?

I'm wondering how many head gasket failures are blamed on a " cracked head " that is really a head gasket failure.

Has anyone cut a cracked head apart for inspection and compared a leaking crack to a non leaking crack?

That's crazy. Mine never exceeds 90c. There's something wrong with your #14 head.

Let me guess. Combustion chamber on my #14 head is breached? I think your gauge is under reporting. I can live with my #14 head.

Btw: Mercedes would not spec the thermostat sensor at 105C to turn on the aux fan if it never goes beyond 90C. I changed it out to a 100C sensor. They can be spec'ed as 100, 105, 110C.

110 C is not uncommon here in So. Cal. in summer with A/C on.

Letting it get up 110c is still crazy in any climate. Mine operates between 80-90c at all times. In 119f heat in Palm Springs mine peaked at 90c with AC on sitting in traffic. And the gauge is perfectly accurate.

Same with mine. A couple weeks back it was 112+ here, still didn't break 100˚ in slow-moving traffic with the A/C cranked. Running >100˚ in any condition indicates a problem, either circulation or fan clutch.

VW diesels of that era are famous for visible cracks, sometimes prodigious gaping ones, between the valves. Those have been cross sectioned and examined and found there is a loooot of meat to have to crack through before there is a problem.
Anyone ever cut one of these up and see how it's made inside?

Did over 4k miles without issues on the cracked infamous #14 head.

10K+ miles since the head install
 

Well, the car just turned 380,000 miles. I have done over 10K miles on the head. It never overheats and uses coolant. If there is any issues with the cylinder cracks then it would have manifested itself long time ago. It seems that my home made pressuring method withstand the test of time.

On a sour note, one of other 300D, also an OM603 engine, has a low compression on cyl 3. It still drives well so I need to decide what to do. It goes to show there is never a cheap MBZ.

I never was happy with the concept that running at 90c over running it at 110c. Was the cause of the cracks.

Instead I have thought it to be operator error. By not giving the engine time before shutting down to moderate any hot spots.

For example coming in off the highway to refuel. Driving right up to the pumps and turning the engine off is asking for issues with a weaker than ideal head casting. Plus you are taking a chance of cooking the oil it the tubos bearing area.

Who really knows? Yet just letting the engine idle first for a few minutes will hurt nothing before shutting down after a hard run.

No no no u can't do this