It's not an unusual problem in the '00-'02 W220s. Because you ran the pump and still saw no pressurization of the struts, you are probably correct.
While you're at it, have your Airmatic relay checked - if it's Hella, you're probably OK. If not, have it replaced with a Hella relay. The relay isn't the source of the particular problem you describe, but will prevent another frequent Airmatic problem - failure of the relay, either causing the pump not to run - or worse, causing it to run excessively, burning it out.
2005 S500 4-Matic
with Gateway 500 iPod integration
1978 450SL restoration project
Formerly: 2000 S500
with Ice>Link iPod integration
Moto V710 phone with MikBox
Upgraded Voice Control