I cant say I unlocked a secret.

It doesn't work very well because most of the time you have to create a weakness in the squad to get the type of player you want.

All I can say is I returned to the game and my 3* squad, and got a 3, 4 & 5 * recommended MC for obvious reasons since I only had 2, weirdly.
I filled out my team but only had 1 GK and got GKs only.
I then had my 3 stooges reinstated, 1 a gk and still I got GKs.
So I bought a 5* GK and got AMR/ST.
I also had not sub wingers at the time.
My friend Peter asked how I avoided GKs and I told him but suggested he wait.
I then had a long exchange with support trying to grab snippets of info.
I told him again and recommended the 2 ST option too.
He got ST recommendations.
He's had GKs ever since apart from when he wanted another ST

As I said I then modified it to try to get a DMC, twice, and I did but only one player each time had DMC and it was a crappy DML/DMC........

Experiences vary but I could replicate this repeatedly. However I'm so over recommendations.

PS. Since the ST nerf (I think) I got a 79T guy that couldn't hit a coo's arse with a banjo. The pain of seeing him in my squad was greater than the waste so I sold him on the market and got 150m for him.....hope things turned out well.