NKJB 1 John 5:
18a
We know that whoever is born of God does not sin;
The main verb is:
does not keep on sinning
ἁμαρτάνει (hamartanei)
Verb - Present Indicative Active - 3rd Person Singular
Strong's 264: Perhaps from a and the base of meros; properly, to miss the mark, i.e. to err, especially to sin.
The secondary verb is the participle:
born
γεγεννημένος (gegennēmenos)
Verb - Perfect Participle Middle or Passive - Nominative Masculine Singular
Strong's 1080: From a variation of genos; to procreate; figuratively, to regenerate.
My paraphrase of 18a:
Having been born of God, he does not routinely sin.
Now onto the next clause:
18b but he who has been born of God keeps himself
The main verb for this clause is:
keeps/protects
τηρεῖ (tērei)
Verb - Present Indicative Active - 3rd Person Singular
Strong's 5083: From teros; to guard, i.e. To note; by implication, to detain; by extension, to withhold; by extension, to withhold.
The secondary verb is the participle:
was born
γεννηθεὶς (gennētheis)
Verb - Aorist Participle Passive - Nominative Masculine Singular
Strong's 1080: From a variation of genos; to procreate; figuratively, to regenerate.
My paraphrase of 18b:
Having had been born of God clearly and distinctly, God protects him.
Does "born" have the same meaning on the two occasions it occurs in 1 John 5:18?"
On both occasions, they are the same Greek lexeme G1080, sharing the same dictionary meaning. They differ in tenses. One is in perfect tense; the other is in the aorist.
OP: It appears to me that the ramifications of how this word is seen cause the difference between "himself" and "him".
This difference in tenses should not affect that since its dictionary semantic remains the same. This bears out in the following statistics:
At https://biblehub.com/1_john/5-18.htm,
5 versions use protects him
5 versions use keep/s himself
7 versions use keeps him