I believe that there are truly selfless deeds. The fact that something produces a benefit does not necessarily make us do such an action for that benefit, that's a sophism. Something can effectively benefit us, however, since that is not the reason why we do the action, then it can be selfless.

When someone sacrifices himself for his children, for his parents, or for people close to him, we can't even affirm that he is being rational, it can be something merely instinctive, therefore, the reason is not in the "benefit" but simply there is no reason. And if there is no reason to do such a thing, we can say that it was a truly selfless act.