Well, no, I don't think it is VAIN repetition at all. That was my point. The passage clearly states that Jesus prayed again, "saying the same words". The second utterance of the prayer is slightly different from the first, but the third utterance is reported as being "the same words" (presumably as the second utterance). If the words were different, why wouldn't the gospel writer record them as such? If it says "the same words", why not just accept it at face value?
Let me approach this question more generally. Can you only say the Lord's Prayer once in your lifetime? Is there something 'magical' about prayer, that a prayer said the first time is effective, but after that is vain repetition? Must you word your prayers differently every time?
I suggest that "vain repetition" means praying thoughtlessly and inattentively. You can do that even with spontaneous prayer, if you are distracted. Conversely, you can pray a formal prayer from your heart, and even repeat it, and it is not 'vain'. What matters is your heart, not your words.