The fact that somebody, or some thing, riding on the hood of the car could easily grab onto the wipers means that the car was a 116-body Mercedes S-class of 1973-80 vintage. Since diesel engines were not available in that model before 1978, “The Princess” was definitely a 1978, 1979, or 1980 model. The next generation Mercedes S-class had recessed wipers tucked under the hood that would be very hard to reach.