Not long joined group and was looking through all the forums about a hydraulic suspension fluid leak on left rear strut. Lots of scary stories were found about what could cause such leaks and cost to fix so I would like to tell you what I went through to fix mine. 2013 c5x7 tourer I bought 2 months ago in a private sale in Spain where I am living but I brought it to the UK last week to visit family. Me to visit not the car. The leak started 3 weeks ago so I thought maybe getting it sorted here might be easier but I'm sure you know the score about dealers and their prices. I have a friend who has a 2 post lift and having not seen him in many years but brought it to his place and he suggested that we start with the simple things. That was to take hydraulic pipe from strut to check that. Replacing the 5p O ring and putting it back solved the problem. Just goes to show start with the simple things first.
Sorry for the long story but I'm sure someone will appreciate it.