On our '91 the rubber couplings and ports have hardened or cracked, and the plastic vacuum tubes have held up well. On on older vehicle, the tubes may fail as well. Even if you fix the problem circuit, you may have imminent failures elsewhere if you don't replace it all. Still, the worst deterioration will occur where there is the most heat, like at the EGR, or physical stress, such as connections from the engine to components mounted on the body.

Steve

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