If the seal of your injectors where they connect to the High Pressure Oil Manifold look like the example picture than you more than likely have a failed, or failing O ring problem in the High Pressure Oil Manifold itself.
High pressure oil in excess of 3,000 psi blasts past the O ring sealing the cup in the High Pressure Oil Manifold and travels along the nipple of the cup into the opening where the injector connects. This eats away at the seal from the top side until it eventually fails.
In the example the seal on the left is New, the seal on the right has been subjected to this condition. As you can see the bulk of the damage is coming from the right which in this case was the top side as it was installed in the injector.
This side should not be exposed to any exterior high pressure oil at all. The only place this can come from is the High Pressure Oil Manifold O ring failure. In most cases by the time the problem is diagnosed properly the cup/nipple is damaged beyond being able to be reused also.
In the past this is only repairable by replacing the entire High Pressure Oil Manifold as a unit from Ford OEM. We have a source to now be able to sell Brand New kits
which consist of (1) Cup/Nipple and O ring. You can rebuild both of your High Pressure Oil Manifolds for what it presently will cost you for one OEM replacement. You will need a specialty removal tool
Any Technician or Powerstroke enthusiast should have this tool in your toolbox. This is a huge problem with 6.0 powerstroke engines, and has gone virtually unnoticed and misdiagnosed for years. Do yourself a favor, If your replacing injectors anyway, REPLACE the High Pressure Oil Manifold Cup/Nipples & O rings at the same time.