OK, so let me give some input on this.
Apalokana, in its noun form, is only found in one context in the Vinaya Piṭaka, that is, in the compound apalokanakamma, “apalokana procedure”, which is one of the four kinds of Sanghakamma. In this context apalokana cannot mean “taking leave” or even “informing”, because this would be counter to the idea of the Sangha making a decision. “A procedure of getting permission”, on the other hand, works well. In this case the Sangha still has the final authority.
It seems to be the case, however, that the apalokanakamma Sanghakamma is a late addition to the Canon. In the Suttavibhaṅga the word is only found once, namely in the vibhaṅga to bhikkhu-pācittiya 79. It is found a further five times in the Samathakkhandhaka (Kd.14), which is likely to be one of the latest chapters of the Khandhakas. (It is the only Khandhaka without an uddāna. Moreover, it contains Abhidhamma style ideas, such as the classification of its content into kusala, akusala, and abyākata.) It seems very likely that the apalokanakamma was adopted by the Sangha after the time of the Buddha, quite possibly by a considerable margin. This, in turn, might well mean that apalokana is used differently in the Vinaya compared to the suttas. We are possibly seeing an evolution in the meaning.
Then there is the verbal form apaloketi. Even in the Vinaya Piṭaka it sometimes means “taking leave”, e.g. in bhikkhu-pārājika 1. Still, even the verbal form often has the sense of “getting permission”, for instance at bhikkhunī-saṅghādisesa 2 and 4, according to which a bhikkhunī needs to apaloketi the relevant authorities before she ordains a criminal. “Getting permission” seems more likely to be correct here than “informing”, and it is certainly better than “taking leave”. A similar argument would seem to hold for bhikkhunī nissaggiya pācittiyas 6-10, as well as bhikkhunī pācittiyas 9, 54, 60, 80, and 94. So this meaning seems to be quite prevalent. In the Khandhakas, however, we do find a number of instances where apaloketi quite clearly means “taking leave” or “informing”, such as where the Kassapa fire worshippers tell their followers that they wish to become disciples of the Buddha.
There are a number of similar instances of both uses of the word, but I suppose this is sufficient to give a sense that there are two fairly distinct usages. So it seems to me that apalokana needs to be translated differently dependent on the context.