I just did air pump job by myself.
My car is W124 400E, my problem was pulley itself, the bearing was completely broken, the pulley was dangling and shaking, it generated a lot of heat and a loud noise, it even toasted the air pump clutch coil.
I ordered a new pulley from internet, I believe it's also available in Fastlane, it cost me 220 USD, the part is acutally a combo which consists of clutch and pulley, it's Mercedes OEM part.
I then losed drive belt, removed two hex bolts, disconnected hoses and removed air pump. Changing pulley and clutch was a piece of cake. I even took apart the whole air pump and gave it a good clean, the whole work took me 4 hours.
After sitting in garage for 2 weeks for parts, my 400E is on road again, thanks to my reliable Ford Explorer!
99 BMW 540i 6-speed 110K Km
03 SAAB 9-5 wagon 80K Km
92 400E (Sold) 245K km
Still missing the days with the Benz, it kept me busy.