Here is what a professor of New testament Greek[Father Mateo] has to Say about Lk 1:28 (Full of grace) and its implications to the immaculate conception.
"The reason why the verb in Ephesians 1:6 does not imply sinless perfection, whereas the form of the same verb in Luke 1:28 does so imply, is this: The two verb forms use
different stems. Every Greek verb has up to nine distinct stems, each expressing a different modality of the verb's lexical meanings.(FH. W. Smyth,
Greek Grammar (Cambridge: Harvard University Press, 1968), 108-109.) Ephesians 1:6 has the first aorist active indicative form,
echaritosen, "he graced, bestowed grace." This form, based on an aorist stem, expresses momentary action,(Blass and DeBrunner,
Greek Grammar of the New Testament (Chicago: University of Chicago Press, 1961), 166. ) action simply brought to pass.(Smyth, sec. 1852:c:1.) It cannot express or imply any fullness of bestowing because "the aorist tense . . . does not show . . . completion with permanent result."(Ibid., sec. 1852:c, note.)
It's Greek to CRI
Luke 1:28 has the perfect passive participle,
kecharitomene. The perfect stem of a Greek verb denotes the "continuance of a completed action";(Blass and DeBrunner, 175.) "completed action with permanent result is denoted by the perfect stem."(Smyth, sec. 1852:b.) On morphological grounds, therefore, it is correct to paraphrase
kecharitomene as "completely, perfectly, enduringly endowed with grace." This becomes clearer when we examine other New Testament examples of verbs in the perfect tense

The next three examples are taken from Blass and DeBrunner, 175-176.)
1. "
He has defiled this sacred place" (Acts 21:28)--their entrance in the past produced defilement as a lasting effect.
2. "The son of the slave woman
was born according to the flesh" (Gal. 4:23)--the perfect with reference to an Old Testament event can mean it retains its exemplary effect.
3. "
Have I not seen Jesus our Lord?" 1 Cor. 9:1, Acts 22:15)--that Paul has seen the Lord is what establishes him permanently as an apostle.
Other examples I found:
1. "God
spoke to Moses" (John 9:29)--the Pharisees hold that the Mosaic Law still and always holds.
2. "It
is finished" (John 19:30)--the work of redemption culminating in the passion and death of Christ is complete and forever enduring .
3 "He
rose on the third day" (1 Cor. 15:4)--unlike Lazarus who was raised from the dead but must die again, Christ rose to everlasting life.
4. "All things
have been created through him and for him" (Col. 1:16)--all creation continually exists, upheld by God (this is the teaching of God's universal providence and also the refutation of deism).
Here are examples, like
kechari-tomene, of perfect participles in the New Testament:
1. "To the praise of his glorious grace, which he bestowed on us in his
beloved"(Eph. 1:6)--Christ is perfectly, completely, endlessly loved by his Father.
2. "
Blessed is the fruit of your womb" (Luke 1:42)--Christ is perfectly and endlessly blessed by God.
Because Luke 1:28 uses the perfect participle
kecharitomene to describe Mary, CRI is wrong to say there is
nothing in this verse to establish the doctrine of the Immaculate Conception. One word of one Bible verse does not
prove the doctrine, but
kecharitomene proves the
harmony of the doctrine[Immaculate conception] with Scripture."