When you say pressure check do you mean the coolant system? If so I would suggest a compression check to see how number 1 compares with the other cylinders.
Also check for any signs of oil floating in the coolant tank and check for water in your oil as indicated by brown muck under the oil fill cap

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88 W124 3.0
96 R129 119eng
06 ML350
98 ML320 sold
02 CLK55 amg