There are lots of potential components that can leak. Yes, the white switches on top of the valve cover can leak, but I doubt they could cause enough of a leak. You need to eliminate one system at a time, whether it is the transmission vacuum system, the EGR circuit, or back to the door lock system. Don't overlook the vacuum check valves, 'y' connectors, vacuum reservoir or even the AC system could have a major leak.

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