Location of Diff Fill plug for 97 E300D
 

I am going to top off the hypoid oil in the rear diff . I have had a slow leak for a while and it's time to check it out. Looked for photo on the forum for location. Could not find one. Just want to make sure I remove the right plug. Is it on the driver's side by the output axle, about 2 inches up from the bottom of the diff? I don't want to manhandle the wrong plug. It looks so clean for a fill plug, just not sure and I could not locate any other fill plugs.

The leak is coming from somewhere on top of the diff, but I can't see it. It's so slow that I'll just fill it until it gets bad, hopefully another 100k miles.

Yes, that's the plug.
If the leak is from the breather on the top of the rear cover, there is I believe a bulletin about this, it involves replacing the rear cover with one with improved internal shielding for the breather.
Gilly