I think the rockheads had plastic/nylon screen material that could be repaired with the proper filler material, don't recall what heat source was recommended. They didn't let me play with too much plastic, 375* rock and oil don't get along well with that stuff.
The one that scares me when I think of it is the nylon nut that hold the spare tire carrier under the wagon. I fixed it with that permatex stuff and then reinforced it with wire a number of years ago.