The 'proper' answer to the question about tightening the vacuum tees is to replace them with a new and tight one, but the previous owner of my car found another solution.

Glue.

I suspect it's something along the lines of Goop, but someone glued all the vacuum lines into the fittings.
It looks like I should be able to pry or peel them out of the fittings if I need to, but they all have this little tracing of some sort of white glue at every joint.

I have had no leaks from any of the fittings so treated, which says something to me.

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-Josh
Testing the cheap Mercedes axiom, one bolt at a time...