Here's a picture of a webasto in an e53.

They are an aux heater that operates with the car off and a small leak when they cycle on to slow cool down fits with your leak area. (If you have it)

Sent from my SM-A528B using Tapatalk

__________________
"When the Team Chief said.... You're trapped in a hole with nothing but a goat and a slinky, what do you do? Stubby said, I'm not sure but it won't end well for the goat...." ~(Overheard) Last day, Phase 3, Q Course