Hello.
I am using Sane from Debian Etch 1.0.14-2.
I have installed the drivers from Brother itself and they work after
fixing the permissions with this lines in /etc/udev/libsane.rules:
# Brother MFC
7420
SYSFS{idVendor}=="04f9", SYSFS{idProduct}=="0180", MODE="664", GROUP="
scanner"
Hope this helps.
Thank you and goodbye!