I'm not positive, but I think that the reason you don't see many 280E W123s in the U.S. is because they either were not sold here or were sold only for a very limited time. Most of the 280Es that you find here are gray market cars.

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Ben

The MBs:
1976 300D (W115) - 330K and still going (sort of)
1991 300D 2.5 Turbo - Sold at 221K
1983 280SEL - Sold at 206K
1981 300SD - Sold at 232K