After getting a P0495 code again (evap canister large leak) I changed the canister vent solenoid. Evidently cleaning out the old valve was not effective. New valve was about $20 from Saturn parts (not available on aftermarket). Took about an hour to install including getting the rear end up on jack stands.
It's been a week and the SES lamp is still off. Either this is the fix of the controller is not meeting conditions for the test. The code was set in hot weather and it has been fairly temperate in NYC this week. Time will tell.
While at Saturn, asked about a locking gas cap. was out of stock but available at $26, about the cost of a siphoned tank of gas and far less than the cost of a cup of sugar in the tank : (