Hi Ran,
Let me start by saying that I am a rookie myself, but I did put in a new Master Cylinder a couple weeks ago in my '67 912. Since nobody else has replied to you, I'll give it a try. The gasket on the old one was pretty much shot on mine so the feeder hose from the reservoir was just loose. I found that the metal end of the feeder hose has a lip on it that popped pretty securely into the top of the new master cylinder. There are no leaks so I'm tempted to believe that's all there is to it.
Now, having said that, remember that these beauties have a single circuit brake system so if that hose comes loose, there go all your brakes save for the emergency.
If someone else can either confirm or correct this, you might save both our skins!
