I have been replacing the 3.5mm (inside diameter) vacuum hoses on my 2001 Passat with silicone from hightempsilicone.com (highly recommended), at $1/ft.

Does anyone know offhand whether this is also the correct size for the smaller lines on the 1996 2.8L 12V V-6 engine?

 

I replaced all mine with the basic rubber hose from Pep Boys... its fine.
And you can get at the hose under the manifold without removing it. Remove the oil stick funnel.