You might try plugging one end of the vac supply line (the solid yellow one) to the master door lock switch in the driver's door. Then use the mity vac to pull vac on the line to make sure it's holding vac. You could have a cracked line, or there is another check valve under the dash that could have gone bad.

You might also try plugging the end of the reservior line and pulling vac to make sure that line is not leaking.

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