Coil cover gaskets/grommets.
 

Replaced coil cover gaskets today after reading about water infiltration, but the originals were in fine shape. The bigger issue I think is making sure that the coil wiring lead grommets in the valve covers are fitted right; they are formed to fit the opening. Replaced plugs last year and found them out of place with water spots in several coil/plug sockets at the firewall. Removing coils can get the grommets out of place pretty easily.

Re: Coil cover gaskets/grommets.
 

What I learned a long time ago is to put a dab of RTV on the grommet and a little on either side before you put the coil cover on.