How did you fix your valve cover leak?

take off cover hammer the flange flat
put back on with new cork... glue it to the cover if you wish with a light smear of sealer
do the little bolts up with a 2 inch long spanner hand tight so that the gasket compresses just a bit
drive it to get it hot
go round the bolts when hot one more time to nip them up if they show any loseness...

job done when they can't be undone with your hand but could be pushed further.... don't do it....with the spanner

they leak becasue they have been done up too tight in the past and the cover flange is no longer flat.
gasket should be compressed no more than about half of its thickness
if you pin each bolt hole down, metal to metal you split the gasket and the areas in between bow up and it leaks as the head and tin expand and contracts
if it just FLOATS on the gasket expansion and contraction is catered for in the soft cork.
the rubber ones just squish out like a slimy mess... twice the price twice the grief...waste of time and effort.

fitting cork gasket is like fitting rope seal anyone can do it but success involves doing it right.

doing it right involves a slight concern that the bolts are not done up tight enough.... if this concern plays in your mind in the days following... you did it right