De-transitivizing morphemes in the tr slot (8)
Several de-transitivizing morphemes can occupy the old object pronoun slot and supplant the y- prefix. I will survey them in order. Two of those — the reflexive and the antipassive (‘unspecified object’) — fit rather naturally into the old object pronoun slot, since they yield an objectless de-transitive clause. A third, the reciprocal, would have fit well in the slot, since much like the reflexive it yields an objectless de-transitive clause. However, when used in its added capacity of marking joint action, it does not de-transitivize the clause, and may thus coexist with an object pronoun.
The fourth de-transitivizing prefix, the new impersonal passive (‘unspecified subject pronoun’, ‘4th person’), is incompatible with an object pronoun slot. So that its introduction into that slot probably contributed to the displacement of Tolowa object pronoun from its traditional slot.
The reflexive prefix. The reflexive morpheme du=- is historically probably the 3rd person deictic pronoun (see Bommelyn 1997). When the reflexive is used, the D-classifier must also be used, as in:
(1)

The reciprocal prefix. Like the reflexive, the reciprocal prefix also requires the use of the D-classifier with it, as in:
(2)

As one can see, in its capacity of marking joint action, this prefix does not fit as well in an object pronoun slot, since — used with a transitive verb — it has to coexist with such an object. In (2e, f) above it has effectively displaced the object pronoun from slot (8). With other verbs, however, the joint-action prefix can itself be displaced to the left-most slot of the verb, the very slot toward which object pronouns seem to gravitate. Thus compare:
(3)

Remnants of the antipassive (‘unspecified object’). The old Athabaskan unspecified-object prefix is unproductive in Tolowa, having all but lexicalized. However, traces of its older function can still be discerned, as in the development of the verb ‘write’ from ‘tattoo’:
(4)

Similarly, in the development of the intransitive ‘drink alcohol’ from the transitive ‘sip’:
(5)

And likewise in the change from the transitive to the intransitive ‘eat’, which can then be re-transitivized:
(6)

The impersonal passive (‘unspecified subject’). With the exception of a few verbs where passivization via the D-classifier still survives, the productive impersonal passive in Tolowa is marked with the prefix tr’u=/’sr in the old object pronoun (tr) slot. Since the object of the transitive remains the syntactic object of this non-promotional passive clause, the tr’u=- prefix can coexist with an object pronoun and displace it from slot (8). Thus consider:
(7)

When the verb includes a locative-adverbial prefix, the growing tendency is to displace the object pronoun all the way to the external slot (14), as in:
(8)

Since the impersonal passive construction is non-promotional, it is only to be expected that it can also be used with intransitive verbs (Givón 1990, ch. 14), as in:
(9)

The Athabaskan object pronoun slot (8) has, as can be seen, undergone consider able re-structuring in Tolowa. The erstwhile obviate object pronoun yu =-, to all intent and purpose, now marks most transitive verbs when both the subject and the object are 3rd persons. But it also marks many complex transitive verbs — those with so-called ‘disjunct’ prefixes — when the object is 1st and 2nd person. Slot (8) may thus be occupied by a transitive marker (yu=-) and three de-transitiv izers (reflexive, reciprocal, passive). It is thus better characterized, in Tolowa, as the transitivity slot (tr).