works fine if you have the right section o ring and yes you need the rod to align plus it holds the valve body against the valve spring pressure making it easier to tighten up the locking collar
if you can easily and cheaply get the correct seals then yes use original but over here they need shipping from the US and postage is often very dear or suppliers won't ship so I often have to think outside the box to repair the ones I have and often have to make new parts or alter a part to accept a new type of seal that is easy to get