Probably leaking from a corroded bead area. The tires will have to be dismounted and the white chalky corrosion removed. May even have to apply some glue especially made for this issue. Then you'll have to have them rebalanced.

You can check this yourself. Pull a wheel off, lay it flat on the ground, and pour some soapy water around the rim. Let it alls ettle down, and then look for small bubbles around the rim.

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Thank You!
Fred
2009 ML350
2004 SL600
2004 SL500
1996 SL600
2002 SLK32
2005 CLK320 cabrio
2003 ML350
1997 C280 Sport