Where are all the /etc/rc#.d-directories
grml doesn't use sysv-rc but file-rc. This means you can configure the init system in one single file named /etc/runlevel.conf with your favourite editor. No symlink-hell anymore.
You can use your favourite editor or update-rc.d(8) to modify it. Read runlevel.conf(5) man page for more information about this file.