Blue thread lock should only be used on metal to metal. It is very aggresive towards certain plastics and will make them brittle.

You dont need thread locker on self tapping plastic, if you really feel the need you can put a small dab of medium ca on the screw but unless you've over torqued the screw and stripped the plastic you are threading into there really isn't often a need.

We dont use thread lock on helicopters with self tapping screws going into plastic and not much vibrates worse than these things.