It's strange, your other car 1988 300CE and my 1989 300CE do not have much rust, at least not to that extent, although they are 7,8 years older.
Are the W124 better rust-protected?

Later on: could you post some pix?

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1996 E320 since 1/16/08, 171K miles as of Feb 2011

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1989 300CE - R.I.P. Dec 29 2007
Other MBs (sold): 1992 300E-24 - 1979 350SLC - 1984 230E - 1990 300CE