“claim that priests on the other hand must be sinless”
There is a difference between being sinless and being simply godly. None of the Apostles were sinless, yet they were godly men, and exhibited the outward evidences of such godliness. Someone who is an unrepentant sinner, such as a serial child molester, is not a godly man.
Does not the Catholic church declare that an unrepentant sinner is de facto, even without any church proclamation, placed outside of communion with the church as long as the condition persists? Does not the Catholic church also hold that those not in communion hold no spiritual authority over believers? Does not the Catholic church also hold that the authority for such things as forgiving sins flows from Christ, through the church, and cannot be found outside of it?
If those things are true, then it appears, by the church’s own doctrines, that a priest who is an unrepentant sinner couldn’t have any power to forgive sins. One might as well ask a nonbeliever to forgive your sins!
The Church declares that the Sacrament of Ordination (Holy Orders), like Baptism, confers an indelible spiritual character and cannot be repeated or conferred temporarily. It is through Holy Orders that the mission entrusted by Christ to his apostles continues to be exercised in the Church.
It is true that someone validly ordained can, for a just reason, be discharged from the obligations and functions linked to ordination, or can be forbidden to exercise them, but he cannot become a layman again in the strict sense because the character imprinted by ordination is forever.
Ultimately, it is Jesus who acts through the ordained minister. The priest's unworthiness cannot prevent Jesus from acting. Light can pass through a dirty window. St. Augustine described it this way:
"As for the proud minister, he is to be ranked with the devil. Christ's gift is not thereby profaned: what flows through him keeps its purity, and what passes through him remains dear and reaches the fertile earth.... The spiritual power of the sacrament is indeed comparable to light: those to be enlightened receive it in its purity, and if it should pass through defiled beings, it is not itself defiled."
Peace be with you
Are you not aware that priests go to Confession too?
In fact, there is a story about a priest who had deteriorated, I believe, into a state of beggar-like existence and was living on the steps of a church. (There was a thread posted about this story.)
Pope John Paul II found out about this priest and invited him to come talk with him. He then ask this priest to hear his Confession.
It brought the priest out of his depression (might have been alcoholism) — in fact John Paul II and most Popes go to Confession weekly.