Let's look:
The words "on your turn" aren't meant as a restriction anymore than on page 192 of the PHB where it says under the section on Actions In Combat "When you take your action on your turn...". Opportunity attacks allow melee attacks in response to a target moving away. The spell grants you a melee attack, therefore the spell can be used for an opportunity attack.
Indeed, let's look: the spell grants you a melee attack
and specifies the conditions under which you can use said attack. You're wrong about the laxity of the restrictions: it's precisely because you
can't take Actions outside your turn that PHB 192 is written that way. You can only take reactions, or resolve a Ready Action (which you took on your turn), if it triggers.
The thing is, you've conflated two questions:
1. Can I do X according to the rules? (X = repeat the VT attack as an OA)
2. Can I do X in my game?
Since the OP explicitly said he's looking for a "solid ruling," he's clearly asking the first question, while you're answering the second (hint: the answer to the second, regardless what X is, is always "yes, so long as your GM allows it.") Further, answering the first actually requires knowing the rules (which leads me to calling out BS on your part: you were derogatory towards people concerned with the rules, since you opened a reply saying "No one likes a rules lawyer.")
The rules provide structure and balance to the game: Rule 0 is the first, of course, but that doesn't trivialize discussing what the rest of the rules allow. Otherwise, WotC wouldn't bother developing them, and just provide fluff and allow a free for all. Many of the rules that seem most arbitrary are precisely to promote balance/bounded accuracy. (I recall a post by a GM
"I tend to judge [rule-bending] based on "are they doing it because it's cool, or because they're sneaking an extra attack in?". Cool gets a nod, power-gaming gets a "nice try".")
Here's an informative/insightful post on
not focusing on the rules. Perfectly legitimate style of play, not what the OP asked.
And that's the last bit of time I waste on this thread...