Mopar Performance valve covers are too wide to seal very well on most heads. You can prove this to yourself with a tape measure. Once you understand the problem you can try and fix it. The only gasket that I've every had any luck sealing with a MP valve covers is the Fel Pro 1612. The 1612 is really thick and it will stand up to the twisting action caused by the valve cover being too wide. If you use a rubber gasket such as the Moroso one it will just twist and shear off. Thinner gaskets will also twist and fail. Good luck, you'll need it. I eventually tossed all of my MP valve covers and found some that were designed correctly. Once I started to use valve covers which were correctly designed all of my valve cover leaks stopped.