I do hope you post what stops your steering wheel clunking noise because my 95 E320 has done this ever since I bought it (it had 87k miles on it then) it now has 157k miles. I've never been able to figure out where that noise is coming from, even had the left front strut replaced under the starmark warranty to try to solve it. No help. My symptoms are exactly as you describe with yours.
I would love to be able to solve this one with my car........