check engine,trac off,vsc lights problem since car 34,000 miles. now 107,000 mil

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have replaced oxygen sensor, vacuum swi valve, R&R canisters. expensive repairs. Now for 5 th time, lights have come back on. Codes: P0440/441/442 indicate small vacuum leak.Leak wasn't apparent. Per dealer, no problems found. They turned off lights, but poor gas mileage. Any help? Dealer says will be very expensive to find the leak. Possible fuel nozzle problem?