Edmond's did a long-term test review of an R class, you might find more information on that site. I remember them complaining about the length of the rear doors, which made ingress/egress difficult in tighter parking situations.

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1982 240 D, 308,000 - 321,127 miles (sold)
1982 300 TD,166,500 - 226,000 miles
1998 E 320, 120,000 - 144,000 miles
2005 C 230 K, 26,000 - 77,000 miles (sold)