So to summarise:
We have concluded that of course United would love another player with Paul Scholes' all-round gifts, but that player probably either doesn't exist or would not be available at an economic price—or at all.
We also believe that they need one "marquee" player to complete the jigsaw and become a truly great team, whether that person is found from within the Old Trafford ranks, is bought young and developed, or is the finished article.
But we conclude that the modern game and United's style have changed and moved on, and whoever that person is must fit in and/or adapt to that style and those tactics and be able to assert playing authority over the game.
We're thinking here of a Michael Ballack, Diego Maradona or Andrea Pirlo-type authority, but not necessarily the same or similar type of player.
Indeed, they have to be a Manchester United-type of player and this is a key point. Why? Because that brings in the factor of a player adapted to United's playing policies, style and tactics.
Take the example of Anderson.
Some people have been bemoaning recently that what Sir Alex has tried to do with Anderson has detracted from what he had and what he did before he joined them.
He was a young, energetic, ball-playing footballer, already likened to Ronaldinho and who loved nothing better than to run at and destroy defenders.
The first thing Sir Alex did was to teach him to tackle. He also got Anderson playing deeper, covering and intercepting.
Of course, that was very different from the way Anderson was brought up, but the manager did want a long-term replacement for Paul Scholes—but not a clone. Scholes has never been able to dribble through a defence in the way that Anderson or Nani and even Ryan Giggs can.
So if Sir Alex had bought Lucas Moura, he would have done exactly the same thing. To understand you need to look at what happens in United's Academy and what Rene Meulensteen brings to the table.
While Rene is now first-team coach, he was originally brought in as technical skills coach. He has a Dutch background and upbringing. What Ferguson wanted was a resource that could instill the way young Dutch players can play, together with all-round technical skill in every department.
So United signed Rafael and Fabio who, although they were playing at wing-back, were natural attacking players. But Rene taught them to tackle better and to stay on their feet. Rafael has also become an excellent header of the ball for his height.
And Chicharito has been taught to drop back into midfield to help out as needed and get hold of the ball as appropriate; he has become better at dribbling; he is found out wide more often and can cross when needed; he can even tackle; and his all-round goal-scoring ability has improved.
Remember, Sir Alex took a rangy, skinny genius with the ball and turned him into Cristiano Ronaldo, one of the finest all-round athletes and arguably the greatest footballer in the world.
So if you look at the United Academy approach, defenders learn to attack; attackers learn to tackle and defend; youngsters are tried out in all the positions on the field; and they come through as all-rounders able to fit with United's highly adaptive style and tactics, which can change spontaneously and as needed during a match.
The solution to how United can replace Paul Scholes and become truly great, therefore, is in fact not to replace him with a Scholes clone. There isn't one. It's not what is needed. The game and United have moved on.
It must be clear by now that United are not, never will be and don't want to become, a Barcelona. Of course they want Barcelona's success.
No, correct that.
They want United's success, as good as it's ever been. Sir Alex is in the process of creating the next truly great team and to do so he needs one last piece of the jigsaw.
So how can he do that? Probably with very different alternatives.
It's not Michael Carrick. He is the pivotal player for the time being and his form this season has been outstanding, possibly leading to him being United's player of the year now Van Persie's form has gone off.
It could be Tom Cleverley. Sir Bobby Charlton was also one of his role models. Cleverley was tried as a left-back and an attacker in the academy before he settled into his midfield berth.
But he's not like Paul Scholes. Now coming back to the levels he was at early last season before his injury troubles, he is a dynamic midfielder who is just as comfortable alongside Carrick as he is bursting forward, linking up with the attackers and even scoring goals.
We have described him before as the "glue" in United's midfield. Together with Carrick they are Sir Alex's first-choice midfield pairing right now.
And you could say that Xavi and Iniesta are Barcelona's "glue." Joe Allen was Swansea's "glue" in a team where there were no household names, but they were a highly effective unit.
If Manchester United are going to go outside to find the one player to complete the jigsaw and make them truly great again, then it is not a Joe Allen. Nor is it a Roy Keane. The game has moved on.
We have frequently mentioned Kevin Strootman as a possible United signing. Most people cite his "box-to-box" and tackling abilities. He could become the key player if he was signed, but again Sir Alex and Rene would work on him and add other dimensions to his game.
On the other hand, Christian Eriksen could very definitely become the answer. He has grown up in Dutch football; he is technically excellent; he has Carrick's calmness; and he fits the mould of recent signings like Kagawa and Van Persie as being highly intelligent in both a footballing and a general sense.
But the one player who does tick all the boxes is surely Luka Modric.
God knows Sir Alex has lauded and coveted him.
Of course he is not the new Paul Scholes, but he can be every bit as effective and perfectly fits United's new style and adaptability.
Does he have the capability to help United become truly great? You bet. Just look at how he transformed Real Madrid after he came on last Tuesday.
It is irrelevant that United only had 10 men on the pitch. It was that ability to inspire, have an immediate impact and transform a Madrid side that looked like they had forgotten how to score that exactly fits what Sir Alex wants.
And whereas while he was at Tottenham there was absolutely no chance of Daniel Levy letting him join United, there is surely every possibility that Sir Alex could get him from Real Madrid and probably for little more than £30 million.
Indeed if the United "money men," whether inside the club or at Nike or Chevrolet, want to complete the package of true greatness and marketability, then Ronaldo and Modric from Real Madrid would do it.
But if it's only Modric that will do nicely.
For the future and inside United's ranks going forward, the successor to Luka Modric could be Nick Powell, Adnan Januzaj, Andreas Pereira or Ben Pearson.