w211 air suspension pump replacement

[puzzler]

Purchased a 2004 E320 wagon with excellent maintenance records one year ago with 94K and now at 120K miles on it, the suspension lost pressure. I noticed it slightly low and then this AM it showed the error message (car too low) and is very low.

Previously I noticed a growly pump sound and was told it may be the power steering, but this happened with the engine off and at intervals while driving. Often when turning on the key there would be a pump sound momentarily and I wondered, Door lock air pump? But now I see it was the suspension pump. Its had the reservoir replaced..Im not sure how often the pump would be expected to actuate normally. Possibly a leaking component somewhere?

Fuse f37 is indicated for this on the chart. Checked all on the row and its good. I also had the window washer quit recently and the fuel gage acts up at times showing full then empty..then it works again. Bad ground possibly..?

Not a difficult replacement on the pump. So if its truly getting power and if it failed replacing this pump should correct the issue..

Could it be the control unit failing to send signal to the air pump? and how often should it be needed to come on in order to keep the system pressurized??

Just getting ready to tear into the repair and ordering parts..

Thanks for the knowlegable comments, in advance..