If heat and pressure are the key, would it possibly be that the system is simply, over-charged by just a bit?

Do make sure your belt is good and the tensioner keeps it tight. (No squeaks when you rev it and release.)

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02 S500
92 500SL
92 400E (Sold)
87 300E (Sold)
83 300D Turbo (Sold)
75 300D (Sold)
74 240D (Sold after 20 years)