Thanks to those who suggested RipIt4Me to back up problem disks. It worked!
For some reason I couldn’t get RipIt4Me or DVD Shrink to copy the files to a new disc, altho they both reported as successful burn. The disc stayed blank(so at least it wasn’t wasted). But I was then able to use DVD Fab to do it, no worries!
Now I’ve just got to sort out the merge/customise problems…