We very seldom replace valve cover gaskets on our Z1's. Most are OEM and have been on & off multiple times. OEM is preferred with Vesrah being a close second.
We apply RTV to both sides of the gasket in as thin a layer as humanly possible. If sealant is squeezing out, too much is being applied. It's difficult to get too little RTV on both sides of a valve cover gasket, but easy to apply too much. We apply a dab of sealant to thumb & index finger, then 'walk' the gasket between them, spreading the sealant as thinly as possible as we go, adding dabs as needed until we get back to where we started.. If the gasket then just looks wet-ish, we go with that. If the mating surfaces are clean & smooth, sealant thickness needs be only a thou or less to seal well. Cleanup at next removal is easy, as the RTV just sort of rolls off in little balls.
On the mating surfaces, we moisten a clean rag with a little motor oil, and wipe both mating surfaces, (head and valve cover) to apply a very light coating of oil, then wipe again with a dry rag. The best rag in the world won't remove all the oil. Doing so leaves a layer of oil likely only a few molecules thick to act as a releasing agent. Cover removal then only requires a few gentle, friendly persuasion taps with a plastic mallet.
We do the end seals as mentioned by Nessim & DrGamma, but install them solid side out. A tiny extra dab of sealant at the corners where they meet the head surface, because it's usually not quite even there.
Something we feel is sometimes overlooked is fastener tightening. Valve cover spec on Z1's. is 70 In.-lbs. We start in the center & work out in a cross pattern, repeating three times; 25 in.-lbs. first, then 50 in.-lbs., finishing the third pass using 70 in.-lbs. A little time-consuming, but no leaks & never a stripped thread.
Good Ridin'
slmjim & Z1BEBE
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