This happened to me on a New Sig Se and I was less than happy. This is how I fixed it. I took a long thin screwdriver and cut a short piece of fuel tubing and slipped over the end. I put a nylon nut into the tubing on the screwdriver. I was then able to thread the motor mount onto the nut held in the tubing. It was delicate... but it worked out well. Once the nut hit the back of the blind nut I was able to tighten it up.