Hi Leo,
congratulations, I guess changing the oil will help to fix the system.
Does the oil smell like motor oil?
Druckregler:
I would spray some multi cleaning fluid like this one
KLICK into it and afterwards dry it with air pressure. Don't forget to clean the little filter as described in the WIKI.
The sealing is not available as a spare part at Mercedes, but it is a standard sealing which can be bought at any dealer for industrial parts.
Grüße
Michael
Meine Galerie