Hydrocarbon test is first on the list. If it has failed it’s likely that the original root cause of HGF was not addressed and that a new gasket was fitted regardless. The gasket is rarely the problem, it is the environment in which the gasket finds itself, there are a number of issues that can cause failure
i) low liner heights, these should be 0.1mm proud of the block surface at room temperature.
2) cylinder head annealed/soft, head surface on the exhaust side of the head should be > 95 brinell, factory hardness is 125 brinell, witnessed by indentation in the surface of the head where the fire ring sits, more prevalent on the exhaust side of the head.
3) casting faults under where the fire ring sits. These are evidenced by small pits around the gasket ring area.
Once the root cause has been identified and corrected the gasket should be reliable.My preference is the Payen BW750 elastomer gasket, the MLS is less tolerant of uneven or low liner heights.
There are fixes for 1 and 3, if 2.. the head requires replacement.
If any or all of the the above 3 are present the HG will fail again in short order.
Oily