Spring Retaining Clips?
BMW uses a neat spring retainer on electrical connectors and the coolant reservoir tank plug. Being a card-carrying Klutz, I've lost a few. So far I have not been able to find a source for them.
I even bought replacement plugs, no clips included, tho.
Hobby mechanic doing my own work for 50 years or so.
We have a 2006 530xi Touring and a 2008 535xi sedan.
I can't really remember the last time I took a car to a repair service.