This was already demonstrated above in showing the three usages, how they use the same grammatical construction and how in two of those usages they explicitly speak of forgiveness of sins.
OK. I couldn’t find them in the thread. Would you mind pointing me to that post, by number, please?
Since you offered no substantive response other than the “liar, liar, pants on fire” defense, I felt no need to reply. The group can clearly see you have no serious refutation.

Hang on, though: the immediate context of the pericope in Mt 18 is “disfellowshipping”. The notion of “forgiveness of sin” isn’t part of that discussion – rather, the question being asked is how to get someone to admit that they’re doing wrong. Even then, the result isn’t “forgiveness of sin”, it’s “you’ve won your brother over” and the relationship with the Church is restored.
Let’s move to the
next pericope, then – the one you’re focusing on: Peter’s question of “how many times should I forgive?” This, too, has nothing to do with the Sacrament of Reconciliation – this is one person forgiving another person.
(Now, I bet that you’re not thinking of the Sacrament of Reconciliation here, but if you’re going to approach a Catholic with the thesis that “Mt 18:18 is all about forgiveness of sins”, then you need to realize that we’re going to respond “nope… no sacramental absolution (a la John 20) here!”
The issue there is the reconciliation of a repentant or unrepentant person to the community.
Fair enough; but, that makes it a question of
excommunication and
restoration of fellowship and not one of “forgiveness of sins”, which is what your claim was.
Not the declaration of doctrine which is in contrast with Christ’s teaching (or in the case of Josephus usage in contrast with Mosaic teaching) which was the usage you were trying to make for Matthew 16 in contrast to the doctrine of Sola Scriptura. So again, note how your original precept is refuted by your own example.
Not seeing what you’re attempting to say here. No, I
don’t see this as undercutting the argument for the divine proxy of authority. Can you be more explicit in what you think you see here?
Then when John paraphrases Matthew’s verbiage (again using the same grammatical construction and linking it with Matthew’s usage for forgiveness and retaining sin in chapter 18)
Except that… John doesn’t. The verbiage of John is completely distinct from that in Matthew! And, considering that “bind and loose” has distinct, legal meaning in the context of the Jewish community (and that this meaning is not “forgiveness of sin”), your argument here really fails to hold. Perhaps you can explain why you think “bind and loose” and “forgive and retain” are meant to be conflated?