No Touch Glass Stripper (got it at Pep Boys) will give you a perfectly clean surface, and then almost any good glass cleaner will work. The No Touch doesn't need to be used very often.

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Alan Weinschel
2001 S500 Capri Blue
2004 E320 4matic Wagon Tectite
1992 300TE 4matic Black Pearl
2000 BMW 540ia Anthracite