Leaking Whirlpool 20RI D4 american fridge freezer

Hi There, can anyone advise on this problem:-
I have just replaced my water filter for the first time on my 20RI D4 fridge freezer. The 1year warranty is out because the fridge wasnt plumbed in until we had replaced our kitchen.

First of all the old filter cartridge was impossible to twist anticlockwise without using pliers on the plastic cap. (i did remove the base grille to get more purchase on the cap but it was still impossible).
When i fitted the new filter cartridge, it was equally difficult to twist clockwise back into position – but it eventually turned using a pair of pliers.

Since replacing the cartridge, I have a steady leak from what appears to be the connection inside the cartridge housing.

I’m looking at buying a new cartridge housing – perhaps that will solve the difficulty in removing and replacing cartridges – or are they all like this?
I assume that the housing is removed rearwards past the fan once the two front screws are undone, so my plan is to remove the filter housing to see where the leak is, before replacing it, if necessary. I’ve been quoted £76 by Whirlpool for the housing – would I need any other parts?
Any advice would be gratefully appreciated.