From the FAQ:

"B6304 Vacuum Hose Replacement [Jim Bowers] I just went through replacing all connections at the vacuum port on my 960. I attempted to get everything from the dealer as in my opinion that system is one of the poorest designs in the car and correct sizes/orientations are critically important. There are about 4 different plastic line sizes and several port sizes for the various destinations. Some need to have a right angle and others are straight. On top of that, the parts illustrations for these little vital parts are very poor in the parts system. I spent a lot of time at the parts counter with many trips to the car to get all the right connectors with the different size ends. Only one connection at the port is made with a section of straight vacuum hose with equal size at each end! My feeling is that getting connectors with the right size ends is important for reliability. When rubber is over stretched is starts cracking real soon. If the connection is loose the obvious will happen. "

That having been said, when you figure this out (with diameters, part numbers, and lengths) let me know so I can update the FAQ with B6304 information.
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See the 700/900 FAQ under 'Select Link' button on the top right.