Most modern valve cover gaskets do not use any sealant, check the covers for
being warped or dimpled at the bolt holes from being over tightened. Make
sure the cyl head drain back areas are not clogged, also.
Do you have spreader bars under the bolt? Are you tightening the bolts to
the recommended spec? Make sure that the bolts do not bottom out or have bad
threads. Make sure that the gasket edge of the cover is flat and that there
is no damage to the head. If all is good and it starts to leak try to
re-torque to spec.
In those years, GM had a pretty sad valve cover gasket
setup. The covers are tin, and if they aren't straight you
can have problems, if someone has overtightened the
bolts and deformed the holes in the valve cover you
can have problems. There was a "spreader" kit that
GM had for those older valve covers. You would get
studs that screwed into the cyl heads, and large spreader
bars that went on top of the valve cover at each hole.
They also had a special set of valve cover gaskets that
you used with the kit. The spreader bars helped to
spread the clamping load over more of the valve
You could also use RTV, but you have to make sure
the mating surfaces are perfectly clean and dry (no
I was fooled by leaky valve covers on a small block once. Turns out all along
it was the oil presure sensor at the rear of the block. Its really hard to
see it and it looks for sure like it the rear of your rocker covers leaking.
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