It is quite easy. You just need to follow a few key steps to do it right. Those steps are:
1) clean all gasket surfaces.
2) use valve cover gasket RTV in the proper locations.
3) use a torque wrench during re-installation.
4) torque down valve cover retaining nuts gradually, and in a crisscross pattern.
5) don't rush, and double check.
1998 BMW 328is
1966 Pontiac GTO
2007 Subaru Impreza 2.5i 5-door
View my photos: Caught in the Wild