Where I used to work we had a couple of smoke machines and I swear by them. They will find vacuum leaks, air leaks, oil leaks, anything you can think of and lead you right to the leak. Also, really not messy to use, no clean up. If you can access one, I recommend it highly. I have found some really obscure leaks I never would have found otherwise on multiple vehicles...and in a few minutes instead of hours.
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Jeff 
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