Thanks for the explanation. Always something to learn on these.

I have heard a smoke generator is the best way to test for vacuum leaks. Shops use them but they are expensive. I built the one shown here DIY How-to: build a vacuum leak detection machine - Pennock's Fiero Forum using a 12v compressor. There is another one that uses a cigar but I found the cigar hard to keep lit and it did not generate enough smoke.
I connected it to the main vacuum line that comes off the rear of the intake plenum.