First, go to the "buy parts" link at the top of this page. Enter your year and search for the fan.

There are three parts involved in pushing air through your vents. The pushbutton unit in the dash generates the signal demanding flow. That signal goes to the fan regulator which is under the glovebox. The regulator feeds the fan.

Find these parts in the catalog. You'll have to know your VIN to see what part you need. The fan and regulator were updated, and the old model is no longer avaliable. If you have an old-model fan, you need an old-model regulator that isn't available, so MB wants you to buy both. But first determine if this is the case.

If it is the case, you can buy both the fan and regulator from this site (or another online site, but this one has good pricess too) for a lot less than the dealer. There's also a hack to install some kind of W140 fan regulator in the older 210, but I've never tried it. I probably will try that when I need a regulator, though. Try searching for that on the forum, if you're interested.