The reason the OE covers leak is from repeated overtightening. This causes dimples where the four bolts go through, and the dimples hold the rest of the cover away from the gasket. It's really very simple to hammer the dimples flat again.

iPd sells (or used to, I don't know the current availability) little gadgets that go under the bolt heads and distribute the pressure over a larger area, effectively preventing future dimples.

I like the cast aluminum covers, but they present their own leaking challenges. There's no lip around the cover, so the gasket is gradually squeezed outwards. Tightening the cover to cure the resulting leaks gradually cuts right through the cork. For these covers, I've had very good results using a rubber gasket instead, and bonding it to the head.