I tried this and it works on my door but I don't have the seal installed and overcenter pressure may be less:
 Take a pair of needlenose Visegrips (Model 6LN), and put two layers of duct tape on the backs of the jaws to protect the collet bore. Insert a 1/8" Allen wrench into the slot at the top of the collet so the short leg sticks up through the actuating drum and the long leg sticks out. Insert the pliers below the wrench until the jaws butt up against the bore of the collet then clamp onto both sides of the bend. Turn.
 When you get it opened could you tell us at what point the Unbrako screw broke? I have a fastbuild door and I noticed that the screw on the forward handle wasn't fully tightened. If the screws were only partway down that might make a big difference in strength.  -Bill Wade