To rest the trueness of your steel ruler just reverse it to it's other edge.. I suspect you knew this. Same reading your golden. Two different readings you can average them.

My guess and it is only a guess that combustion escaping and driving coolant out of the area. Allowed the head in that area you find warped to get very hot. So hot it may have let the metal collapse a little and that is the reason you found the loose head bolts.

The whole engine may not have overheated to enable this. Generally described as a hot spot where coolant is driven away from the location.

The reason actually it does no harm coming off the highway. To let the engine run for a minute or two before shutting down. Reduces possible thermal stress on the casting. This occurs when there is too much temperature difference between parts of the casting.

I have suspected for a long time that if you practice this delayed shut down on a 603 with the number fourteen head. It may last a lot longer. It certainly will do no harm if practiced.

Also I think I would employ a water wetter if I owned one of those heads. Or any Mercedes diesel with an alloy head.

The area of issue on your head has undergone a lot of thermal stress and should be checked for cracks in the area. Also do not exceed the maximum of head material removal as it is limited on these heads. A thicker compensating head gasket may be available. This could allow a little more material removal than allowed or make up for the amount of material removed. This also might mean your may not have to shim your pre chambers.

Although they will have to be removed for milling the head. The break you may be getting depending on the last owner is the rest of the head may be flat.

I have purchased cars where the owner shut the car off when all the coolant was blown out. On a couple where they continued driving the head was warped beyond sensible salvation. Last but not least make sure that wherever you take the head knows what they are doing. Usually asking any local Mercedes dealer where they send theirs out to is fairly reliable. Or even an independent mechanic that does a lot of Mercedes. If nothing else they know where not to send them.