Changing it is definitely a good idea if it hasn't been done yet. However, keep in mind that the new fluid color will turn dark very quickly as well. It just does that! I used Febi-Bilstein hydraulic fluid as well, which is OEM and can be purchased online instead of the dealer for much cheaper. Good place is ***************. It think it's like $8 vs. $20 plus at the dealer. It takes less than a liter to replace the reservoir. Here is a link: http://www.***************/search/product.aspx?sid=1xjvai55s5ag1tiuhsipm555&makeid=800016@Mercedes&modelid=1387605@E320%204MATIC&year=2002&cid=98@Fluids%20%26%20Chemicals&gid=7607@Hydraulic/Suspension%20Fluid