Last owner apparently not a big fan of changing the oil

-- The valve cover gasket isn't the source of the "sucking" sound, _ _ _ a "sucking" sound, could just be the un-silenced noise of the air being drawn into the carburetor. If it is not that, it has to be a vacuum leak in the induction system --
-- Yep !! - Also check to see if the carb, and intake are tight.