Yes, the one on the right side of the engine behind the cylinder head is the one. It has a small handle on it for removing it, fairly easy to get to. The transmission one is in the same area, but much lower and harder to get to, and has the familiar "lock" that has to be broken to remove the cap.
What do you mean that the advisor "was no help"?
Did you ask for a headlight alignment, or ask how to do it yourself, or what? There is usually info in the owners manual concerning headlight alignment. Usually you want this done with an optical headlight aligner, but the "old fashioned" methods still will work. Does your E320 have Xenon lights or not?
If you are planning on doing an "extra" oil change (between the Maintenance Commitment "free" oil changes) then be sure to used a MB approved synthetic oil, and I'd recommend the MB oil filter too.