How to revert to factory uboot of Goflex Net

I want to rerevert to the factory uboot of Goflex Net. How can can I read the factory uboot back from flash rootfs partition and write it to flash? Is it necessary to change the uboot environment variables which were changed during installation of new uboot? I don't have any mtdblock devices in /dev.

I found out how to do that after Debian was booted from a USB Stick:

mknod /dev/mtdblock2 b 31 2
mount -t jffs2 -o ro /dev/mtdblock2 /mnt
cp /mnt/uboot-original-mtd0.kwb /root
umount /dev/mtdblock2
apt-get install mtd-utils

# the next commands could brick the device if something is wrong
cd /root
flash_erase /dev/mtd0 0 4
nandwrite /dev/mtd0 uboot-original-mtd0.kwb
reboot

#after reboot ssh-login shall be possible -> activate hbmgr
mount -o remount,rw / # remount rootfs writeable
vi /etc/init.d/rcS
#uncomment the line with "/etc/init.d/hbmgr.sh start"
reboot