Maybe my take on the Rashford situation is naive. If we were willing for Barcelona to take him for £27mil, why not cut the price to £10-£15mil and therefore give any club who's interested more of a chance of meeting Rashford's financial demands?
City and Liverpool both had fire sales in the past when Klopp and Guardiola joined to get rid of players they didn't want at the club. Same for Rashford, move him on, take a hit on the transfer fee but just get him out and close the chapter on his career as a Utd player.
Get Zirkzee out on a loan with a obligation to buy, therefore the money is coming albeit next summer.
Lastly a few of us have said it, It's are utterly hopeless at exploiting the free transfer market. Even if you need someone with experience in just for 12-24 months to tide you over. Get them in.