I tried the rain x washer fluid and it seemed to smear and did not work well. I siphoned it out after a few uses. I only tried it because the rain x glass treatment worked so well. I still use the glass treatment, but won't use that fluid again.

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07 E350 4Matic wagon, 06 S430 4Matic, 99 SLK 230
retired W210 (x3), W124, W126