Hi I think most times, it is that the plastic pulls away from the glass as the plasticizer evaporates. There are issues of mold attacking but I don't think this is the common failure that looks like fern leaves. I would suspect that one can protect a CRT that one expected might have troubles by carefully sealing the edges of the front shield with RTV. One might consider a repair by placing the CRT in a vacuum chamber such that their was some of that windshield repair fluid in a small dam around the edge. One would pump it out for at least one day and then while under the vacuum pour the repair stuff around it. Then release the vacuum and allow the repair stuff to be pulled into the glass. Not an easy process but it might work. Dwight