[BenFenner]

I am happy to explain.

It is not an "issue" per se, it is simply an obvious area for improvement over the factory unit (just like aluminum is over magnesium+coating). Other than cost, I see no reason not to include the spark plug tubes in the valve cover itself. It would eliminate 8 o-rings from the engine and with them, 8 different potential oil leaks. I see no downsides (again, except price to manufacture) to incorporating them.