I usually start with the #4 valve because it's the hardest to get at and the one you get to when the engine is coolest, to get the quietest adjustment possible on that one. With all the valve cover stuff you've been doing your oil leak, like emsvitil said, is most likely the half moon. Lousy luck on those grommets.
This is a good idea.
The over-tightening of the rocker cover is difficult for me to understand. First, the cover would have to deflect. It is cast, its not going to deflect or bend very much if at all. The force necessary to actually pull up and bend the rocker rack by the studs in the rack would have to be very great. So, I don't think the noise was the rockers contacting the top of the rocker rack.... but I know it's been said that it can happen.
I got a feeling that the noise (sounds like louder than normal rocker tick) is actually the cam profile, the cam may be causing a little more valve noise? Or slightly worn rockers or shafts allowing the rockers to clatter?
I know from experience that the valve lash setting can have a big affect on the sound of rockers, as well as throttle response, at least for two cam profiles - Toyota stock and the 261C.
OR.... possibly the head, valves, cam, rockers just need more break-in time?