The damage shown in the photos is simply the plastic (my guess is it is Delrin) breaking down from UV exposure. Back in the 80's I built my own circular polarized antennas for 70cm and 2M for AO-13. Having a lathe I made some parts from white Delrin (a nylon like material). After about ten years it showed the same UV damage. Note that the black plastic element insulators in the photos are not cracked. The black pigment used in the element insulators apparently protects them from UV. After learning this lesson I started using the black Delrin for my home brew antennas and have had no problems with UV damage. All that said, some plastics are more resistant to UV than others. I have two M2 antennas in use for terrestrial use and after ten years of being up in the elements they are both working well. Note that the UV damage may not have gone all the way to the core of the component yet. If it is still mechanically intact (and just looks awful), it can be salvaged by coating it with a thick black sealant and covering that with black electrical tape.
--73-- Dave WA0AUQ