I replaced mine yesterday. The gaskets are held in place with two bolts and simply slide off the solenoid. You just remove the connector from the solenoid, slide off the old one and slide on the new one. The one of the right side of the engine is harder to remove because theres more stuff in the way but with some patience you can do it. The left one is easy once you remove the air filter ductwork.
My local O'Reilly Auto Parts had the oem gaskets for $10 ea. They're hard plastic with a rubber center sleeve.