I need new bushes for my car too but as I understand it they aren't available separately as they are bonded to the anti-roll bar. May be different on the E270 as mine is an E55.
My car has had a creak / knock from the front pretty much since I bought it 3.5 years ago (car was on 38K now on 72K). MB replaced lots of front end suspension components inc both front airmatic struts (thankfully under warranty) but no improvement! It has driven me mad!
Just recently I took my car to Andy and Paul at Eurocharged and they test drove my car to do some data logging. I didn't mention the issue but on their return Andy said about the creaking / knocking and put it up on the lift. There was nothing obvious but he thought the bushes looked like they were debonding from the bar. I did some searching and there were a few threads on the mbworld site with E55's having similar issues and that a high pressure spray grease solved it!? I have therefore since lubed the bushes (I gave it a good dosage of Wurth HHS 2000) and I would say 80% of the noise and knocking has gone! This lubrication is only a temporary measure and was just done to be sure it was these bushes that were the problem. Thanks to Andy we now know what needs to be done