Here's a Mercedes in Montana that might have maybe possibly belonged to John Bonham. It's an interesting vehicle nonetheless, but I would assume that Bonham would have some sort of muscle car or sports car and not a boring sedan.
The window etching on both rear windows is kind of compelling to me. I would assume that could be something Mercedes Benz might do for a celebrity.
Correction: Swan Song Records was started in 1974, so I doubt a '72 Benz would have that from the factory.