That you can find pro Roman excerpts is not surprising, but you fail to quote from later works where he has certainly CHANGED his views.
"The scholastic doctors argue about whether Christ was born from sinful or clean flesh, or whether from the foundation of the world God preserved a pure bit of flesh from which Christ was to be born. I reply, therefore, that Christ was truly born from true and natural flesh and human blood which was corrupted by original sin in Adam, but in such a way that it could be healed. Thus we, who are encompassed by sinful flesh, believe and hope that on the day of our redemption the flesh will be purged of and separated from all infirmities, from death, and from disgrace; for sin and death are separable evils.
Accordingly, when it came to the Virgin and that drop of virginal blood, what the angel said was fulfilled: “The Holy Spirit will come upon you and overshadow you” (Luke 1:35). To be sure, the Messiah was not born by the power of flesh and blood, as is stated in John ( cf. 1:13): “Not of blood nor of the will of a man, etc.” Nevertheless, He wanted to be born from the mass of the flesh and from that corrupted blood. But in the moment of the Virgin’s conception the Holy Spirit purged and sanctified the sinful mass and wiped out the poison of the devil and death, which is sin. Although death remained in that flesh on our account, the leaven of sin was nevertheless purged out, and it became the purest flesh, purified by the Holy Spirit and united with the divine nature in one Person. Therefore it is truly human nature no different from what it is in us. And Christ is the Son of Adam and of his seed and flesh, but, as has been stated, with the Holy Spirit overshadowing it, active in it, and purging it, in order that it might be fit for this most innocent conception and the pure and holy birth by which we were to be purged and freed from sin. [LW 7:12]"
http://beggarsallreformation.blogspot.com/2005/12/luther-on-immaculate-conception.html
“I reply, therefore, that Christ was truly born from true and natural flesh and human blood which was corrupted by original sin in Adam, but in such a way that it could be healed.”
Well of course it can be healed, such is what occurs after our death and resurrection.
The problem is that this denies that Christ was sinless. Thanks for posting this. I wondered how Luther got around the problem, and I see that rather than deny that Mary was the Theotokos, he has her passing on her sinfulness to Christ.
Again, it all fits together. If Christ were truly sinless, than so is Mary. If Christ were truly God and Man together, than Mary is the mother of God.