Dirt on an oring is the usual culprit if all the orings are new, unless you dinged one during the change. That is rare, so I would put money on a piece of dirt. The leak between the halves is fairly rare with that fat oring. Take it off and inspect it for blemishes and to see if there is a piece of dirt stuck in it. Clean the surfaces it comes in contact with and make sure there are no burrs.
Your powertube leak is probably not all the fault of the oring. It may have some slight differences from the original one that was in there, which is why it leaks when the original one didn't, but I suspect that the leak is actually occuring because your powertube spacer is too long. Even the original oring you have installed may develop a periodic leak after a while as the sear wears a bit more. Keep an eye on it.
Except for the Automag in front, its usually the man behind the equipment that counts.