Jeff, I'm not an EE, but did suffer through a couple terms of electrical engineering. Miserable stuff.
The little circuit diagram really just shows the pin connections, which I believe you have right. The round thing, lower left, is the coil, the pair of horizontal parallel lines on the left is the ignition condenser, etc., so it's no help as far as figuring out how the relay works.
Within the relay there are 3 transistors (the black things), a bunch of resistors and probably a couple of capacitors. Any of them could be bad and render the relay inoperative. Unfortunately, none appear to be obviously fried. To diagnose it, you need someone who knows how to test each of these components.
You might be able to find a technician at an electronics repair shop to do that for you, but it might be more expensive than buying a new relay. Wouldn't hurt to ask a couple, though. Another thought is to find someone with a similar relay and try it in your car before spending big bucks. Or try to scrounge up a used one from a Benz dismantler and try it out.
Good luck!
George Davis
'69 280 SL Euro manual