Your die seems to be a simple piece of ply wood and well used enough to a wear mark where it meets the extruded. Have you tried putting a thin piece of rubber in the wear marks? The rubber should act as a seal and prevent the bleed out. You can probably take some liquid gasket maker like permatex and paint it on if you don’t want to cut a piece of rubber.
It's so much pressure that it tends to be more work than it's worth to try to prevent the blowout. I am planning on making a new die that fits inside the hopper to see if that helps.
