Here's an article that has several Patristic quotes and an excerpt from St. John Maximovich' wonderful book The Life of the Virgin Mary, Theotokos
“Original Sin” and the Mother of God
By a Priest of the Orthodox Church in America
First: The use of the term the stain of Original Sin is exclusive Roman Catholic Church terminology and is NOT Orthodox.
The Orthodox position is that we are all born into a sinful world made sinful by the Fall of Adam. No one is or ever has been conceived and born with a “stain” resulting from Adam’s sin. In her lifetime, the Blessed Virgin Mary did not sin by her own choice with the help of the Holy Spirit.
Because Roman Catholic doctrine teaches that all people bear the stain and guilt of original sin from the moment of their conception in the womb, the Roman Catholic Church had to devise a “Doctrine of Immaculate Conception” to confirm that the Holy Mother was sinless because, the Vatican rationalized, our Lord could not be born of someone sinful. The immaculate conception doctrine makes her different from the rest of humankind; it makes her not fully human because she was not by her own choice sinless but by the will of God. If Mary were sinless by God’s choice, not hers, then by virtue of the fact that she was as fully human as all of humankind is and has been, then God could make us all sinless and take away the free will given to us by our being created in His image and likeness.
The following is from the book Life of the Virgin Mary, The Theotokos by Blessed John Maximovitch, published by Holy Apostles Convent, Buena Vista, CA:
The Heterodox Teaching
of “Immaculate Conception” and “Original Sin”
“Saint Ambrose (339-397), Bishop of Milan, comments that, ‘Of all those born of women, there is not a single one who is perfectly holy, apart from the Lord Jesus Christ...’
“The Orthodox Church teaches that the Virgin Mary was conceived by Joachim’s seed and the period of gestation was nine months. None of the ancient holy Fathers (ed.—only the Roman Catholic Church) say that God in miraculous fashion purified the Virgin Mary while yet in Anna’s womb. Only Jesus Christ is completely pure of every sin, while all men, being born of Adam, have borne a flesh subject to the law of sin. Many have correctly indicated that the Virgin Mary, just as all men, endured a battle with sinfulness, but was victorious over temptations and was saved by her Divine Son.”
Blessed John Maximovitch (1896-1966) affirms that The Church teaches that "through the fall of Adam and Eve, all of the human race inherited death, becoming enslaved to the devil through the passions. The progeny of Adam and Eve are not guilty of their first parents’ tasting of the fruit; we are not being punished for this first sin or 'original sin.' If, for the sake of argument, we maintain the invalid heterodox teaching that the Theotokos was preserved from this 'original sin,' that would make God unmerciful and unjust. If God preserved her, why then does He not purify all men? But then that would have meant saving men before their birth, apart from their will. This teaching would then deny all her virtues. After all, if Mary, even in the womb of Anna, when she could not even desire anything either good or evil, was preserved by God’s grace from every impurity, and then by that grace was preserved from sin even after her birth, then in what does her virtue consist? She would have been placed in the state of being unable to sin.
“The Virgin, as a true daughter of Adam and Eve, also inherited death. She was not in a state of never being able to die. Thus, St. John of Damascus writes on the occasion of her Dormition, ‘O pure Virgin, sprung from mortal loins, thine end was conformable to nature.’"
Blessed Archbishop John continues to comment that the Virgin was not placed in the state of being unable to sin, but continued to take care for her salvation and overcame all temptations. The righteousness and sanctity of the Virgin Mary was manifested in the fact that she, being “human with passions—like us,” so loved God and gave herself over to Him, that by her purity she was exalted above all other creatures. Mary was to become the Mother of God, the Theotokos, not because she was to give birth to divinity, but that through her the Word became true man, God-Man.
The last comment made by St. John is so important -- “Mary was to become the Mother of God, the Theotokos, not because she was to give birth to divinity, but that through her the Word became true man, God-Man”.
If the Holy Virgin Mary’s human will was interfered with (ed.—as in Roman Catholic doctrine) She would not be totally human and therefore Jesus Christ would not be totally man (ed.—human) and totally God.”http://aggreen.net/theotokos/orig_sin.html