(no subject)

...In Germanic and Romance, the perfects formed from the past
participle had either the verb 'to have' (OE _habban_, German
_haben_, French _avoir_) or the verb 'to be' (OE _wesan_, German
_sein_, French _être_) as the auxiliary. The usage of the verb 'to
be' is restricted to intransitive and reflexive verbs. When the
past participle agrees, it agrees with the subject if the auxiliary
is the verb 'to be', and with the object if the auxiliary is 'to
have'.

I expect Greek follows the same pattern - would anyone here care to
fill in the gap...

The Modern Greek perfect employs the present tense exw, "to have"
with the third-person singular of the dependent (called the non-
finite; Modern Greek has no formal infinitive), which is formed on
the perfective stem as is the future/subjunctive. For example, to
say "I have read it to him" you would say "Tou to exw diabasei."

The pluperfect uses the imperfect/aorist form of exw, so to say "I
had read it to him, you would use "Tou to eixa diabasei."

The auxilliary always agrees with the subject, and the pronoun is
only employed for emphasis. Other than that, it is all very similar
to French, German, English etc. and fits with what you have been
saying.