How fast should the master vac line leak at the nipples?
 

My car is very slow to shutoff. I have already identified that the replacement ignition vac switch needs to be replaces (ignition broke internally recently). I hooked up the mighty vac to the nipple on the line and it was very slow to build pressure. Is this normal? As everyone else can probably say, I have broken the nipple and glued it back on several times, I wonder if it is plugged or this is normal behavior?

None?
 

If you are attaching a Mity-Vac to one of the nipples on the main vacuum line and trying to pull a vacuum it may take a bit of pumping with the Mity-Vac to empty all the air in the line and brake booster. Once you do get a vacuum it should hold without any discernable leakage. Of course I would cap the other nipple on the line to rule out leaks elsewhere in the system. Since you have a manual transmission you may already have the other nipple capped off.

I was attaching the mighty vac and running the engine. No leaks but it built up really slowly. I am wondering if something is in the valve clogging it.

That's different then. Whatever it builds up to it should hold that when you shut the engine off. If it does that eliminates a leak as the suspect. If there's no leaks I would suspect a weak pump, especially if it does the same thing at the other nipple. If the vacuum build much more quickly at the other nipple then it is entirely likely the nipple in question could be clogged.

One the of oft-mentioned online articles about setting the transmission vacuum gives a drill size for reaming the orifice in the nipple when it gets clogged. Of course I don't remember if they are both the same size or which site the article was on. You could always try poking at it with a paper clip.

Which nipple?
The one closest to the pump?
I believe the other one has a reduction of some sort. Seemingly not, see below.
But I'll check 'em.
OK, both immediately to 21. (warm engine)
The one closest to the pump takes a few seconds to reach 24. The other one needs to be hooked up to shut off the engine, on mine (CD) anyway.

Heh you two nipple folks.

But that is what I was looking for, almost certainly something in there plugging it up. In other news I found that one of the lines into the fw was leaking and another that I had previously unhooked was not. The outcome? Heat on my feet yaaaaaaaaaaay!