the hole in the block can be drilled out, and a brass sleeve glued into the block, you need to be accurate, and the brass must be a good fit on the leg, this is a fix i have used for many years with this tyoe of undercart mount, i have had a look at my instruction master, and the cowl blocks are mentioned, page 11, illustration 52
bit of chinese english, but is there, bottom left hand corner of the illsustration that refers to the cowl, although it calls it a conopy, IF we have the same instructions, that is!!!!