Thank you for all your replies. I'll start by checking the timing chain stretch on the engine. Is the easiest way to check for stretch is to use a timing light and if it is off by 5 deg on M103 then it's time to replace it? Is this correct?

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200 75 W115 (Mom's)
190e 90 2.6 W201
E320 95 Wagon W124
72 BMW 3.0 CSI