There is a different seal for the two different types of thermostat. If the thermostat is mounted vertically you have a later type engine, if it is mounted horizontally you have an early engine.

__________________
1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine