Trevarrick,
There are usually soft closers fitted to each and every Drawer runner.
If the door on your 400 pull out is Hinged on 1 side only, then softclosers on 1 side will be adequate.
If the door is connected to the pull out mechanisim, then 1 each side would be better to keep the door from having un-even pressure exerted on it.
Snezza.