The round pins on final stage resistor connector are known to loosen internally after years. Renew the female pins on the connector or at least use some oxide contact cleaner and then contact paste on them. (I once had a problem of non-responding blower caused by poor contact on that very same connector and it was the low voltage PWM activation line. There have even been cases where the plastics have caught fire because of heat up due to contact resistance.)

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E39 530dA -02 M-Sport Messing metallic
E53 X5 3.0dA -06 Sport Stratus grey
E70 X5 40d -12 M-Sport Space grey