valve covers that won't leak - ??

Well I'm on my 4th attempt trying to get my valve covers to not leak. My valve covers (stock covers) are not perfectly straight but I hammered them out (where the bolts are) before each time and made sure all surfaces were clean.
1) purchased the Mopar Performance steel core rubber coated valve cover gaskets and installed with no RTV. Leaked at the back corner near the firewall on both covers
2) reused the steel core rubber coated gaskets after cleaning them and the valve covers and used RTV on the gasket to valve cover side. Leaked at the back corner near the firewall on both covers.
3) hung the rubber coated gaskets on the garage wall and bought Felpro cork gaskets but didn't use any sealant. Leaked at the back corner near the firewall on both covers
4) bought another pair of Felpro cork gaskets and this time (today) used Gasgacinch between the valve cover and gasket as well as along the back corner near the firewall on each head. Will wait 24hrs before going for a test drive but I'm hoping the 4th time will be a charm.