what really is happening. injectors dont have a wiper seal, so the oring lets it slide by, and build up just keeps happening. If it had a wiper, IE a square edged seal, it would wipe as it was pushed. Regardless of the plastic brand you almost always get the buildup. Ultramolds uses a wiping o ring in there shooting star, reason it don't have to be cleaned all the time.
What else does not help, I see all the time, is shooting the plastic way to cold and man handling on the injector to shoot it, Inevitably pushing the plastic by the orings as well.