The clamp could not have made any difference. The reason there is no clamp from the factory was because it was not needed. The connection is a vacuum connection. It is constantly sucking the hose so the hose is constantly under pressure to stay on the connection point.

Later 450 and 280's, the 110 were full of vacuum connections. None of them ever had a clamp. When the engine is running they are difficult to pull off.

So the lack of a clamp was a cost issue.

But back to the idle situation: I think after the valve adjustment the engine ran correctly. But previous owners, who didn't want to take on the task of adjusting the valves, just tweaked the idle adjustment to compensate for an engine that was not idling as it should. They thought adjusting the idle would fix the 'problem'. No, you fixed the problem. Now you must correct their short-cut moves.

And using the crow's foot is the way to go. The special tool you mentioned is supposed to be used with a torque wrench when doing the adjustment. If moving the adjustment screw doesn't take enough pressure then the screw is not going to hold. That way you know that screw needs replacement with an oversized one that, at least at one time, was available from Mercedes.

I doubt they sold many of these replacements. I don't know of anyone who ever had an adjustment screw work loose. I guess they could.

And the special tool? I have seen a few of these. They have always been ground down a bit as the original tool is a bit too fat to fit. So mechanics will grind off a few mm from the outside face. It makes all the difference in the world.