I also own a 2001 E320T. My approved fluid booklet dated October 2000 (which may have changed by now) lists three different approved hydraulic oils for various MB's:

For the 600 sedan, MB part no. 100 890 00 11
For the load leveling system, hydropneumatic suspension, hydraulic soft top, 4matic, ASD, MB part no. 000 989 91 03 10
For tandem pumps with common oil reservoir for steering and level control in E-class, Model Year 1996 (aka W210 vehicles), MB part no. 001 989 20 03 01

I assume that each oil has different additives to handle the specific application, with the 210 oil having to work with the self leveling system and power steering. My guess is that non-purists just buy the generic Febi oil (for the 124's) and use it in the 210's. Similar to when I worked on 600s with bad hydraulic systems and would find that PO or previous mechanic would have substituted ATF in place of the approved (and very expensive even in the 80's) MB oil. Costly mistake. Common wisdom on 124's which should be applicable to 210's would be to change the fluid and filter at the resevoir every 2 to 4 years. In my experience, there is a big difference in the color of clean fluid and used fluid. I have not changed mine yet but I expect to soon. I will let you know how it goes. Mark