A full bead of rtv should not leak if it is done correctly. Use lacquer thinner to clean the surfaces (not paint thinner). After you bolt down the intake, make sure to stick your finger down the distributor hole and press the fresh rtv away from the distributor hole. Then give it over night to dry.
with a breather and pvc valve there isn't that much pressure under the intake even on a poorly sealing engine. so the rtv should hold if every thing is clean before putting on the rtv.
to check for engine blow by, start the engine, pull off the pvc and breather and place you hands/fingers over the valve cover holes for 5 or 10 seconds. then release one hole and see how much pressure has built up.
how many miles on the engine now. What did you do to freshen it up?
what compression and cam size?