I must admit I've never liked Ven Nanavira's chariot argument. He seems to be reading a very mechanical interpretation into what it seems to me are instructions on how to contemplate currently arising phenomena. But perhaps it is not surprising that he picks on the mechanical aspect when the simile happens to be a chariot...
An important question to ask is whether translating
paramattha sacca as ''truth in the highest, or ultimate, or absolute, sense' is accurate, or whether it invokes too much intellectual baggage.
The Vissudimagga passage he is commenting on is, as I read it, practical instructions on the development of insight. It says, in part, (Nanamoli translation pp687-688, XVIII.25-28):
... he defines all states of the three planes, the eighteen elements, twelve bases, five aggregates in the double way as 'mentality-materiality', and he concludes that over and above mere mentality-materiality there is nothing else that is a being or a person or a deity or a Brahma. ...
So this is in the meditative context of breaking down every aspect of experience, and in that context:
... just as ... in the ultimate sense when each part is examined, there is no chariot ...
... when each component is examined there is no being as a basis for the assumption "I am'...
The meditator looks carefully and finds no "I" there... Just phenomena...
Perhaps we are veering too far off the original topic, but does Ven. Nanavira explain
his method of seeing through "I"? That might shed light on his thinking...
Mike