Of the radiators that failed.

What antifreeze were you using?

One of the technical advisors in the Mercedes Benz Club of America, a chemist by degree did an analysis of the various antifreezes available. The Mercedes antifreeze remains PH neutral thoughout its life. This prevents the deterioration of the plastic that makes up the radiator.
Use Mercedes antifreeze and you won't have a problem with the radiator.
86300SDL 275,000 miles, original radiator.
82 300TD radiator replaced at 160,000 mi Center section collapsed
88 560SL only 90,000 miles original radiator
All my cars have Mercedes antifreeze and only Mercedes antifeeze, even the 65 Mustang.

Dave

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car