When you pull the intake this time, look for
oil on top of the intake valves. If there is
oil there, look for
oil in the intake runner, especially on the bottom. By look I mean feel.
Since you will have the valve covers off, you can squirt oil right on the valves (through the springs). See if you can prove the valves are leaking or rule them out.
PS
While the intake and gaskets are off, you should check the intake angle. When people mill heads down, they also need to mill the angle on the intake.
Blykins can better describe the best way to do this check, but here's my attempt. Set the intake on with the old gasket on one side. No gasket the other side. Snug up the side with a gasket. Then use feeler gauges to measure the gap between the head and intake on the non gasket side. Check at the top and bottom on both ends (gap should be the same top and bottom). Everything should be clean, so if the old gasket has RTV ect on it use a new gasket.
I have heard of other methods, that I cannot recall. I think there should be a way to use silly putty, but I have not done this. You would need to be careful not to let any drop into the oil drains, so maybe not a good idea.