1) How do you guys find part numbers for these tiny parts?

2) The part I need is a plastic washer that goes over the power seat control for the seat back. This is a stock photo, so it's NOT at the red arrow, but just down and left of the green button. On that round stub there's a plastic washer that goes over it. I guess its job is to keep the entire plastic trim piece around these controls from moving forward.

https://cdn4.pelicanparts.com/techarticles/Mercedes-W124/120-ELEC-Power_Seat_Control_Switch_Replacement/images_med/pic03.jpg

1991 300d