Ok,
I'm having some progress over here. I have been looking at the lid assembly (I have 4 to play with) and noticing that all but one of of the clear parts (with the tube that holds the gas bulb) is warped. When cleaning the empties, I was very careful not to use hot water on the bottles as I read that they will melt easily. I was not so careful with the lids
I used sodium percarbonate and boiling water to soak the entire lid assembly (except for one which I had already cleaned seperately when I emptied the beer from it. The others I got from a mate in one go)
Here's a pic of one of the batch that got the boiling water:
After using the only part that wasn't warped, I managed to get it to seal and the bottle got rock hard with the gas. Happy days
Still not a 100% success as when I pressed the tap only the gas came out. The plastic tube was attached to the lid and everything seemed in place but no liquid at all came out of the tap itself.
I will come back to this experiment later as I am getting sick of it for now
I am also stripping the heads of the triangle screws by using s 2mm flathead screwdriver. I have a triangular tool coming in the mail (hopefully) soon.