I understand you say this because as an apparent Calvinist you hold to OSAS, but besides that issue and texts to the contrary, we are dealing with RCs here, in which to be faithful to the faith they once received excludes them from salvation unless they repent from such aspects as believing they will finally realize salvation by atoning for sins and becoming good enough in Purgatory. And instead come to God as damned and destitute sinners and cast all their faith on the risen Lord Jesus to save them on His account, by His sinless shed blood.
As to "Once Saved, Always Saved," there is so much Scripture that positively undergirds that viewpoint, with only a few rather weak and cloudy or ambiguous passages that may be interpreted to support either OSAS or Arminianism, that brings me to the conclusions as follows:
(A) If the term "everlasting life" or "eternal life" can ever cease through the will of the giver or the recipient, it is not eternal and any Scripture employing it would be meaningless.
(B) If a (hu)man can lose his/her salvation through passive mindset or active rejection, then keeping it inherently requires engagement in beneficial works, which is "earning one's way to heaven," with the reward of salvation bestowed only when death terminates one's earthly occupations of mind and body; rather than being a free gift bestowed at the outset of conversion.
(C) IF (and no doctrine should be based on a conditional statement of this kind) I should be brought up again before the Eternal Judge by the Accuser of the Brethren as to having fallen and violated one or another or several of the ordinances of the law whether unwittingly or deliberately, I would be found guilty, would lose my salvation, be again condemned to Hell, without hope of ever getting it back again. If so, I guarantee you both of us have already lost our salvation forever.
(A) and (B) are conjoint stipulations, which places the burden (C) of being saved on the works of the (hu)man no matter how minute the prerequisite, and thus God's Grace can no longer be free to the recipient of it.
I choose OSAS as the only justifiable Scriptural alternative, and if I am wrong, in this I will not have made a mistake.
In actuality, it is only the regenerated one who knows (ἐπιγινώσκω = epiginōskō = totally conversant with, through prolonged personal experience) the permanence and life-changing effect of the indwelling Spirit of Christ, who would never choose otherwise.