FYI I read somewhere on here or another forum that this is actually caused by or at least in part by the hand lotions significant others use before getting in the vehicle. A startling number of ppl have seen this ONLY on the passenger side handle where their wives sit...
If this is true you may or may not see it depending on your situation. Or your hand lotion tendencies
I can neither confirm or deny this as my wife's car does not have the handle on the driver door, and the passenger door does suffer from this but we've had the car over 10 yrs so certainly she has sat on the passenger side when I drive...
Haven't seen it in my X5 yet but she is rarely in there.