Well, the head gasket (or the head itself) contains three things:
so if the head gasket has failed, you'd think there would have to be a violation of a boundary. So, we'd be talking about:
- Coolant leak to the outside of the head
- Oil leak to the outside of the head
- Compression leak to the outside of the head
Or some combination of the things being contained:
- Oil in the coolant - visual
- Coolant in the oil - possibly visual
- Compression in the coolant - bubbles/spewing (or coolant in the cylinder - white smoke)
- Compression in the oil - blowby (or oil in the cylinder - blue smoke)
So if you suspect a head gasket or head warpage problem, checking for these indications comes to mind.
The other thing that could happen is a failure or blockage of the oil or coolant somewhere, such as inside the head. This would lead to overheating and damage. Not all that likely to be a blockage. For oil you should still have a good pressure gauge indication and might see oil spray if you open the oil filler cap while running.
For coolant, you need good coolant circulation - especially by way of the water pump. On many cars you can open the radiator cap and verify coolant motion when the throttle is kicked. Not so on the "no radiator cap" Mercedes radiators.
I'm trying to think of what the initial overheat might damage, leading to continuing overheating - that's not the head gasket/seal. Just because the head gasket is leaking a little bit, it would not necessarily grossly overheat.
Are you overheating while driving, or just sitting there idling?