For anyone following later, Samba is broken as it needs write access to /var/cache/samba,
I cured this by adding the following line to FSTAB, and it now works in RO Mode
tmpfs /var/cache/samba tmpfs nodev,nosuid,size=40M,mode=1777 0 0
I also needed to create /var/log/samba and start the SMBD service after a reboot