I don't have a way to make plastic new, but I've had good results with
WD40 for restoring surfaces with WD40. Some plastics get dusty and
highly ablative on the surface with age and environment. Plastic LOVES
WD40, if it is 'thirsty' Coat the plastic with WD40, and wait. It
will soak in, sometimes it takes an overnight. Repeat this until the
plastic no longer 'drinks' the WD40. You've done all you can do now
with this method.
I don't know that it restores the original strength of plastic, I doubt
that, but it sure helps with the surfaces' appearance and wear
resistence.
Best,
Jeff