I had the same problem with my 300E. My body man cut out the rusted out areas, welded heavy washers around the jack tube and re finished the both sides of the car. The cost was more than I expected, about $900 but was worth it to me because it was done right and it looks great!

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Donwo
1999 SL 500 Sport (30K miles)
1998 E320 (SOLD)
1989 560SL (SOLD)
1987 300E (TOTALED)
1986 300E (SOLD)
1984 300SD (SOLD)