I am milling my metal , and after oxidation according to the manufacturer's instructions , I aplly a layer of bonder . I use the one from Bredent. I have zero issues . I use Ivoclar Inline .
Some of these milling alloys "eat" opaque !! I would try a base coat of GC metal bond or the Bredent equivalent. With Straumann`s "Coron" i just sand-blast , ultrasonic and opaque (GC metal bond base coat first ) Also have a friend that uses this a lot and fires first coat at 1000`C - he says it prevents bubbles when using EX3 !