The Loctite type thread locker liquids harden in the absence of oxygen, thus they are called anarobic; in the absence of oxygen. It may be difficult to understand, but some plastics are porous to the migration of oxygen. The plastic bottle the liquid Loctite comes in is a prime example. That is another reason not to use Loctite with plastic type materials. I do believe I recently read of a thread locker that was compatible with plastic type materials. I love the statement "The only constant in life is change".