The engine is back in and I've actually fired her up

All gaskets seem to be sealing nicely except the right hand rocker cover one. The covers are original and a bit battered, and they did have sealant on the old gaskets when I removed them. Would I be better off keeping these original covers and using sealant again, or replacing for lower quality new covers? And any preferance on sealant if thats the way to go?
thanks
Paul