Thank you....  I found the problem.

4 mm ID silicone hose is the best way to replace aging small-bore rubber hose.
I've replaced just about all the 4 mm hose in my 1983 turbo c900, and it
does improve things when it replaces hose that's cracking and/or splitting
and has some leaks.

Craig.

Another thing to look at as well as the hose itself is the fitting where it
connects to the manifold. It's common for crankcase vent nipples to not make
a good seal as the rubber grommets tend to harden and crack with continually
heating and cooling of the engine. The vacuum nipple, while not subjected to
quite the same level of heating/cooling as the engine block and cylinder
head itself, certainly gets hot and over time the grommet will stop making a
proper seal. They're cheap to replace for places like PFS, etc. of any of
the other online Saab parts suppliers.

There is probably a better way to do those vacuum connections, and it could
well be possible to tap a thread in the grommet hole of the manifold and
install some sort of a machined brass fitting onto which the vacuum lines to
the brake booster, etc. can attach, but to date I haven't see it attempted.
I don't know if the cast aluminium of the intake manifolds on the 8V or 16V
engines has enough aluminium cast around the grommet hole to support
something threaded into it, but if someone has done this, please let us
know!

As an aside I'm still trying to find brass or similar alloy replacements for
the high-temp AC cutout swtich t-housing that mounts in the middle of the
upper radiator hose in my 8V cars. Do the 16V engines utilise a
similarly-mounted thermoswitch mounted in the top radiator hose?

Craig.