You can test for leaks by just looking for cracks or hardened rubber. As an active test, spraying something non-combustible (e.g. water or rubbing alcohol) at suspect points should cause a change in idle speed, momentarily, at a leak point.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7