[metmom]

Scripture, please, to support the claim that being in grace equates to sinlessness.....

[Wyrd bið ful aræd]

I would presume that the justification is not scriptural, but mathematical (sola scriptura doesn't exclude math, does it?)

To be full of grace (or full of anything), a person or object cannot contain any amount of another substance, else it is by definition not full of grace (or whatever the substance in question is).

[redleghunter]

Scripture, please, to support the claim that being in grace equates to sinlessness.....

Your statement above gets to the heart of "Whose Righteousness or whose righteousness is The Father seeing?

Of course in Whom He is well pleased!