you need to replace all of the all of them or they will all leak over time i think there are 12 dont go to mercedes they will charge you $5k. There are many private shops that can do it. I just had my 2001 sl 500 done for $1000.
Call "TOPHYDRAULICS.COM and talk to them before you spend a Dime. They have video and instructions posted on DIY removal and installation of cylinders and you can also find valuable info videos on YouTube. Once they are rebuilt a good mechanic can reinstall for way less than a dealer if you don't want to do it yourself. Either way, it's cheaper than going to the dealer who will start calculating charges before your wheels clear his driveway.
Very easy to replace seals on hydrolic actuator. There are several videos on you tube that will show you step by step instructions. I have already did 6 of them. Takes about an hour and costs about 50$ for kit at mbseals.com. Good luck!