2001 E53 X5 Passenger door open alert, even when closed
 

So it started intermittently: the chime warning for 'door open' plus the interior lights would come on briefly on left hand bends. The dash showed it was the passenger (right hand side) door that was opening enough to trigger the sensor. As soon as the corner was completed the dash indication would go off again.

I thought it might be something I could adjust out, but of course I put it off.

Well, now the door either claims to be open the whole time or (worse) constantly triggering the chime and interior lights.
Some basic googling seems to show that the microswitch is inside the door lock actuator mechanism - and I'd really rather not have to replace that. Is there some method of adjustment I can try? or is there any chance that silicone spray shot in any available aperture of the mech will help?

Unfortunately, there are no mechanical switches inside in the door lock mechanisms - they are all hall-effect sensors (a type of magnetic switch), so no amount of spray lube or cleaner will change their operation.

Either the lock mechanism is not actually closing properly (in which case some cleaning/lube spray may help*) or the sensor is faulty, probably requiring replacement of the entire lock mechanism.

One other possibly is a wiring fault or a fault in the driver's door switch module, which acts as a controller for both front doors. Maybe check for water damage on this module?

Did anyone work on window regulator lately?

Sometimes, the door lock actuator was not reconnected properly.

PS: If you suspect door actuator, then serach for a used unit on ebay or local junkyard.
PN for Left FRont door is 51218402537.