Minor point - it should be: change /etc/usbmount/usbmount.conf ...
I think you also need apt-get install ntfs-3g if ntfs-3g is to be included in the FILESYSTEMS list.
Apart from that, moving to that newer usbmount seems to have nailed it - thanks.
I need to do a clean install, just to be sure.
I have notes
Download the temporary Raspbian Buster + Rachel image -
Temporarily at ...
http://rachelfriends.org/downloads/public_ftp/rachelpi_64EN/rachelpi_2019/rachel-pi_kolibi_buster_unofficial.7z
Is that still the best place to be getting it?