I remember seeing something on "Shadetree Mechanic" where they introduced a product that injects smoke into the vacuum system (engine off). With the right lighting you can see the smoke seep out at the leak points.

The most popular way is pretty much the way you descibed, by spraying solvent at suspect areas. In addition to brake cleaner and ether, you can use starter fluid or flow propane over suspect areas.

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95 E320 Cabriolet, 169K