Drilling a small hole (3mms or so) at the start of the crack will put a stop to their spread. Then the patching can begin.
I took a section off the corner of a catcher once and tithe small gap resulted in clippings spitting out. I had to put electrical tape over it and it has held ever since. I just wish I knew the drilling trick before.

Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!