We bought the lad for £18m and since being with us he has proved that he can perform at the top level. There is no doubt that Masch is the most effective defensive midfielder in world footballer. He has his faults though, he is an incredibly bad passer of the ball so not too good in open play.
On top of that, as was previously said, Masch is most effective against the bigger teams, but Rafa feels obliged to throw him in against some of the less footballing sides where he doesn't add anything to Liverpool.
If Barca came in with an outrageouse offer of, say £40m, then it would make sense to sell.
Who we could buy - I don't know. You are not going to get a carbon copy of Masch, and to be honest, you don't want a carbon copy, you need someone who is better on the deck.
Bottom line - if he is to go, he should leave on our terms