You fixed nothing. It is called notes; commentary not additions.
The word in verse 8 and Christ in verses 7 and 6 are being used synonymously. The word equals Christ because it is of and through Christ.
Christ, the word in the heart and mouth, that is, (In other words) what was just stated Christ, the word in the heart and mouth is the word of faith in which we preach.
What is the word of Faith in which we preach? Christ, through which the word is in the heart and mouth.
What is even more interesting is Romans 10:6-8 is a paraphrase of Deut 30: 11-14. Those who received this letter would of known this and made another connection as they compared the two.
And the LORD thy God will circumcise thine heart, and the heart of thy seed, to love the LORD thy God with all thine heart, and with all thy soul, that thou mayest live.
(Deu 30:6 KJV)
If thou shalt hearken unto the voice of the LORD thy God, to keep his commandments and his statutes which are written in this book of the law, and if thou turn unto the LORD thy God with all thine heart, and with all thy soul. For this commandment which I command thee this day (to hearken unto the voice of the LORD thy God, to keep his commandments and his statutes which are written in this book of the law), it is not hidden from thee, neither is it far off. It is not in heaven, that thou shouldest say, Who shall go up for us to heaven, and bring it unto us, that we may hear it, and do it? Neither is it beyond the sea, that thou shouldest say, Who shall go over the sea for us, and bring it unto us, that we may hear it, and do it? But the word (his commandments and his statutes which are written in this book of the law) is very nigh unto thee, in thy mouth, and in thy heart, that thou mayest do it.
(Deu 30:10-14 KJV)
They would have noticed the word, the commandment and statutes written in the book of the Law are the same word mentioned in Romans in which and through Christ has been placed in the heart and mouth.
What is even more Interesting is the prophecy in Deut 30:10-14 is being spoken in the presence tense. So the Gift of Christ in the Heart, through which His word, his commandments and his statutes which are written in this book of the law are in the heart and mouth was available at the beginning of Moses Ministry if not before.
Since Israel refused the gift. God through Jeremiah repeated it in other words as the New Covenant.
But this shall be the covenant that I will make with the house of Israel; After those days, saith the LORD, I will put my law in their inward parts, and write it in their hearts; and will be their God, and they shall be my people.
(Jer 31:33 KJV)