Run a search for "stop light switch" or "brake light switch." It's an $18 part that you can install yourself in about half an hour, and is the frequent culprit of the ASR/BAS light coming on. That repair was the first thing that this forum helped me fix on my '98 E-class. There's a ton of info, and even the most novice DIY'er can change out the switch himself. If that's your problem, as it so often is on the W210, you'll be fine in no time.

Cheers, John

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'98 E300TD (W210) | Sold 6/09 with 205k and counting
'04 VW Touareg V10TDI