Thanks again tjts1, I decided to not jump the relay in fear of tripping up some software, and just pulled the air pump which is so easy except for the nut on the air line, and figuring out the release tabs on the wire connectors. But my pump is indeed fried, stinks of electrical fire and has grinding bearings. No function when connected to 12V. I'll get another ordered and hopefully be good as new soon, and when the air line came free it STILL held significant pressure so whatever leak there was is very slow.

As many others report the tube was cracked allowing dirt into the compressor right at the inlet. The rubber is still soft and supple, looks like rough installation work which I find all over this car, misaligned tabs and misfitted plastic parts just shoved together.

I only guess the dirt caused the bearing to fail and that burned up the electric motor. The compressor cylinder seems fine although that rebuild looks like a great idea.
Thanks for the notes on ride height. Yes, just as well.

I also steered away from the 4matic and went for 2wd hoping for better MPG and that e350 engine is WAY too complicated..Scares me to even think of it. But they do produce a nice MPG. Beautiful cars..

Thanks for the link, great for further follow up.