Maybe the car you have had the engine head machined
while gaskets where replaced(several times before you bought the car ???) down to its limits and now as well when the gasket
was replaced. Can you measure the height of
the head in your engine to see if is within limits-
maybe somoene who has the same engine here online can
measure theirs and you can compare .
Previously I had a 190E mercedes and they machined
the head by 3mm way beyond "normal" which caused etxtreme pressure increase and constant damage to the main gasket.
Michael, Poland