The last possibility most folks dont tend to check due to it being a rare one is VTC phaser ring. This is exacerbated by how long you've had a failing gasket. Most owners tend to put about 5k + miles on a failing gasket until something is changed or the problem gets worse
He's a thread I made about it, I only had a NEW bank 1 phaser which I took the opportunity to measure and it seems like tooth 5 alings with one of the tooth of the phaser. As you can see in the thread the failed VTC has a ring that has shifted by one tooth yet looks like normal VTC.
https://www.myg37.com/forums/engine-...ml#post4315666