In the past I've documented Luther's view of the Immaculate Conception. As far as I can tell, Luther post-1527 did not believe that Mary was free from sin from the moment of her conception. His post-1527 comments typically refer to something happening to Mary at her conception of Christ.
While reading Bonaventure today I came across the following:
1. Finally, the cure of original sin takes place in this way. It is cured as regards guilt, but the temporal punishment remains, as appears in baptized infants; it is cured as regards eternal punishment, but the actual inclination of concupiscence remains; it is cured in the parent, but even so, transmitted to offspring by the very one who was healed in baptism. Its stain is blotted out, but its consequences remain, to be fought against as long as life lasts; for in no human being, assuredly, has concupiscence ever been extinguished by ordinary grace. We say this because in the case of the Blessed Virgin, concupiscence was extinguished by extraordinary grace when she conceived the Son of God.-snip-
4. Finally, because temporal affliction denotes a condition which affects the flesh: as the flesh always remains subject to some form of infection, so also it must always remain liable to penalty. Hence, as grace does not remove the penalty and corruption from the flesh, so also the consequences of original sin - concupiscence and bodily weakness-may coexist with healing grace. Concupiscence may gradually decrease, but its roots remain. No wayfarer, then, is completely rid of it, except the most Blessed Virgin, who was relieved by a special favor. Because the Virgin conceived Him who is Expiation of all sin, she received a privilege that radically freed her from concupiscence, so that her conception of the Son of God would be all-pure and perfect.-snip-
"It was wholly right that the Virgin should shine with a purity greater than any other that could be thought of under God. For it was to her that the Father determined to give His only Son - born of His heart, equal to Him, and dear to Him as His own Self - to be the one and self-same Son of both the Father and the Virgin; the Son Himself chose to make her His true Mother; and the Holy Spirit willed, and made it be, that the Son from whom He Himself proceeds should be conceived by her and born of her. [source]
Now, generosity is appropriated to the Holy Spirit, and so is the sanctification of the Virgin in whose womb the Word was conceived. Therefore, although the incarnation is the work of the whole Trinity, by appropriation we say that the Virgin conceived of the Holy Spirit.-snip-
Next, there must be completeness in the manner of conceiving. Of the four possible ways of producing man, three had already been followed: first, out of neither man nor woman, as with Adam; then, out of man but not woman, as with Eve; third, out of both man and woman, as with all those born of concupiscence. For the completion of the universe, a fourth way must be introduced: out of woman without the seed of man, through the power of the supreme Maker.And yesterday, I came across the following from John of Damascus:
Again, there must be completeness in the power itself. Hence, in the production of the Son of God, three powers concurred: the natural, the infused, and the uncreated. The natural power furnished the material element; the infused power set it apart by cleansing it; the uncreated power brought about instantly what a created power can achieve only gradually.141
Thus, the Blessed Virgin became a Mother in the most complete sense, for, without man, she conceived the Son of God through the action of the Holy Spirit. Because the love of the Holy Spirit burned so intensely in her soul, the power of the Holy Spirit wrought marvels in her flesh, by means of grace prompting, assisting, and elevating her nature as required for this wondrous conception.
So then, after the assent of the holy Virgin, the Holy Spirit descended on her, according to the word of the Lord which the angel spake, purifying her, and granting her power to receive the divinity of the Word, and likewise power to bring forth. And then was she overshadowed by the enhypostatic Wisdom and Power of the most high God, the Son of God Who is or like essence with the Father as of Divine seed, and from her holy and most pure blood He formed flesh animated with the spirit of reason and thought, the first-fruits of our compound nature not by procreation but by creation through the Holy Spirit: not developing the fashion of the body by gradual additions but perfecting it at once, He Himself, the very Word of God, standing to the flesh in the relation of subsistence. For the divine Word was not made one with flesh that had an independent preexistence, but taking up His abode in the womb of the holy Virgin, He unreservedy in His own subsistence took upon Himself through the pure blood of the eternal Virgin a body of flesh animated with the spirit of reason and thought, thus assuming to Himself the first-fruits of man's compound nature, Himself, the Word, having become a subsistence in the flesh. So that He is at once flesh, and at the same time flesh of God the Word, and likewise flesh animated, possessing both reason and thought. Wherefore we speak not of man as having become God, but of God as having become Man. For being by nature perfect God, He naturally became likewise perfect Man: and did not change His nature nor make the dispensation an empty show, but became, without confusion or change or division, one in subsistence with the flesh, which was conceived of the holy Virgin, and animated with reason and thought, and had found existence in Him, while He did not change the nature of His divinity into the essence of flesh, nor the essence of flesh into the nature of His divinity, and did not make one compound nature out of His divine nature and the human nature He had assumed. [source]Now I must confess to never having studied the Mariology of either of these two men. I assume some Roman Catholic could (or will) put forth a host of citations corralled together as "proof" both of these men believed in Mary's immaculate conception. I don't have the time for that debate now. My only purpose here is to document the similarities between these statements and Luther's statements.