I don't know about W140 seats, but consider that there are at least 5 varieties of US W126 seats -- manual headrest, power headrest, memory, heated and orthopedic, . I don't know if the differences are in the seat or external controllers. I'm sure my memory seats don't have heater coils or lumbar bladders. There are other variations such as upholstery material.
SEC seats might be an option.