I like to remove the injector lines. Takes 10 minutes, maximum, and they are out of the way.

They don't use any o-rings. Just a tapered seat. Make sure you start the nuts by hand. If they won't make a full turn by hand, then force the tubes until they bend and the nut is properly lined up. The worst thing is to force it with a wrench.

For the valve cover, the proper torque of 11 ft.-lb. is rather critical to properly seal the gasket. If you are too loose, the gasket leaks. If you are too tight, you bend the valve cover and the gasket leaks.