Need a brake booster or rebuild kit

[Benzilla]

I just purchased a 1967, 110% original, Mercedes 250S, with all the documentation since day one, including the shipping from Germany. However, when I push the brakes, I hear this vacuum sound and the engine idles down (like you opened a vacuum to the intake). Anyway, I'm in search of a rebuilt booster assembly for it or a rebuild kit. Anyone know where I might find one?
The pads are good and evrything else is good. The car runs and drives great but there's no "Power assist" with the brakes, being the diamphram is leaking. I might be selling it cheap if I can't find one. Interested? Request pics if you are.

 

[wireman]

I have no idea where you will get one from but I believe your diagnosis is correct in the servo diaphragm has failed, this failiure is often caused by a defective (leaky) non return valve in the vacuum pick off from the manifold which allows a lung full of petrol vapour to enter the servo as the engine is stopped, the petrol attacks the servo diaphagm in next to no time.

If you do repair your servo make sure you check the valve for leaking.
Many years ago I was unaware of this and ended up repairing it twice in one month.

Watch out for the big long "jack in a box" spring inside the servo chamber.