I managed to pick up a 1987 copy of Glass's guide, which covers the 1976-1987 (mid year).
One of the things that was interesting is the resale value of Mercedes-Benz models at the time. Generally they held up much better than the current ones do, except for the 6.9.
Suppose you wanted to buy a 1979 6.9 - a car that was then only 8 years old.
You would have paid $45,000 for your trouble, on a car that cost $80,650.
However, had you wanted a more regular 450SEL (4.5) that car would be...