Quote Originally Posted by Bas View Post
Hence "last resort". I'll definitely try the vice grip/brute force method first. If all fails and I irreperably ruin the threading in the plastic, I can also just tie-wrap that thing down tightly.
No, there are other choices. You could use a tap to thread the plastic to a larger thread size and use different machine screws. Or you could use self-tapping sheet metal screws.