There is also the possibility that you have a mismatched pan/timing cover. Until I think '74 or so chevy used a thin front pan to cover seal . Later they changed to a thicker seal. Most gasket sets come with a diagram to show how to tell which one you need as well as both seals. anyway, if you use the thin seal on an engine that takes the thick seal it will dribble when oil starts slinging or if OVERFILLED. May not be it at all but something to check. Some gasket companys offer a one piece seal/pan gasket for pre 85engines. they are expensive but seal great.