I've used basic toothpaste to polish my glass lenses before. I had a coating start to flake a lot, and I took it all the way off (very slowly) with just my fingers and toothpaste. To this day (couple of years), not a problem with the clarity.

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1982 240D, sold 9/17/2008
1987 300D TurboW124.133 - 603.960, 722.317 - Smoke Silver Metallic / Medium Red (702/177), acquired 8/15/2009
262,715 and counting