the gasket is the seal for the cover, if there is no leak,

you don't need to change it. Changing the o-ring for the distributor cap is very easy. You don't even need a tool. Just unplug the spark cables connector to the distributor cap (you must remember the order), and loosen the clips which attach the cap to the distributor body. Honda might use bolts instead. You should see the o-ring which seal the cap. If it is cracked, you can change it. The parts should be pretty cheap. The valve clearance might not be necessary.