Do a search and you'll find plenty of info.

Here's one for starters:

http://www.xoutpost.com/bmw-sav-foru...pring-diy.html

You probably have a leak and if your X has got some miles on it, over 50K, then you should consider replacing both. I just had a leak on the same strut and decided to replace both, after I had the shop confirm the leak.

Good luck!