I don't know how any of this is "secret". It's pretty simple. The credit card companies make a lot of money. They will do everything in their power to continue to make a lot of money. Either play by their rules (which most people will) or don't use them.

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2009 ML320 Bluetec
1985 300CD
1981 300TD

Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD