did u put glue all around the interface or u just put at the curves? i did mine and glued only at the curves and it works fine. but i also have seen some glued all over the interface. for me it doesn't matter as long as there's no leaking.
i don't think there's problem with your valve cover. anyway i got the used valve cover from the chop shop for 450. my old one was broken by a f@#$%^& mechanic from a workshop in jalan ipoh.