You dont mention the year for your vehicle, but check out the following website for several years available for your vehicle.
According to my MB manual the oil capacity for the E320 with the L104 (straight six cylinder) engine is: 7.4 US quarts (or 7 metric liters)
13mm for motor oil on E320
215/65 R16
217 HP
Do I have to use MB power steering fluid or can I use an alternative fluid in a 1997 E320.
For a 2000 Mercedes E320, it's recommended to use synthetic motor oil with a viscosity rating of 5W-40 or 0W-40, complying with MB 229.3 or MB 229.5 specifications. Brands like Mobil 1, Castrol, and Shell Rotella offer suitable options. Always check your owner’s manual for specific recommendations and any updates on oil specifications.
0w-40 Mobil 1 synthetic is recommended by mb
See the related link below for step by step instructions with pictures on how to change the transmission fluid in your 1999 MB E320.
under the top cover, on top of the engine
MB steering gear fluid
I have a MB 2002 E320. There is a little button to push on each side of the seat.You cant see it but feel for it toward the back of the side seat.
Use whatever Mercedes Benz recommends. If you do not have an owners manual contact a MB dealer.