I bought a Canadian E420 that had been brought into the US. The speedometer had been changed to MPH. The car had all of the records including the speedo swap. When I did a "car fax" I got a red warning on mileage. I compared the original km numbers to the new miles numbers. They were perfect. So the downside seems to be with Carfax.
Anziani
'87 300E 180K
'95 E420 Special Edition 99K