I'm familiar with the pre-Sprinter MB vans. Yahoo has a Sprinter group with lots of info. MB vans, including Sprinters, do not have a great reputation for rust resistance. Living in the salt air of Florida, I'd look closely for rust problems on a used Sprinter.
Sprinters have had consistent problems with the EGR valves and they are known for eating up brake pads. Apart from those issues I don't recall reading of any other known widespread problems.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13