What torque setting and sequence did you use? Did you ever go back and re-torque? Do the valve cover screws have sleeves like the oem screws? If all torqued correctly and no sleeves on hardware, seems like the gaskets could be compressing unevenly/incorrectly. Do you know where specifically it is blowing out?
Does the aluminum cover have the standoffs on the bottom like the oem cover does? I haven’t seen a good image of the bottom of the aluminum one. If the gasket is not seeing the same levels of compression as with the oem cover, I could easily see this being/becoming a common problem with the oem gasket.
The lack of standoffs to set height and gasket compression would be squarely where I would put my money. I have a feeling this will be a common problem on these valve covers.
I’m not a design engineer, but the oem screw sleeves act as crush washers and prevent the plastic oem cover being drawn down onto the head beyond a certain point. That height was certainly “engineered” and the only reasons for that would be to prevent cracking of the plastic cover and to ensure a very specific amount of compression on the gasket. Too little clamping and air would pass between the gasket and the head. Too much and the gasket will squeeze out, also allowing air to pass between the gasket and the head. This is the reason why I suspect oem screws and sleeves would likely solve the problem. Adding weld and remachining in addition to the sleeved screws would be best imo, but would be much more involved and unattainable for most owners.
