The early style sump plate without the drain plug was used on the bus.
the one with the drain plug was for the beetle. the logic was that
on the bus VW wanted to make sure that everytime you changed to oil,
the filter screen would be cleaned. VW felt that the 1600 motor
worked harder in a bus and wanted to compensate by making sure that
the screen was always cleaned. the only was to change to oil
was to remove the entire plate. this is how it was for a period of
time, i'm not sure of specifics or dates...and i'm sure many sump plates
that didn't have drain plugs were quickly swaped out for ones that had
drain plugs...

patrick
86'crewcab