HaVoC373- I know I've been more lurking then commenting, but your despair is heartbreaking. I won't say I'm an expert at molding and casting, but I do have years of experience with what's happening to you and I wish I could be there to help you, but alas, I'm in the US. Although I have been giving thought to moving to London as of late to work on Doctor Who.
I have what i think is a fairly simple solution, but it will sound complicated to you, please bear with me as I explain. The molds you made have too many parts to try to cast at once, your flow patterns are good, but you need to inject the urethane (resin) into the mold to force pressure behind the flow. The main thing necessary to get air bubbles out is a Pressure pot. In the US we tend to buy modified paint pots, not entirely the safest of options, but it works. A medium compressor for air is needed as well. Again, in the US these two purchases ran me about $200. But for you I can't say. The effect you need is the high pressure to collapse the air pockets inside the mold. You inject the urethane, then leave the tube in the mold and fill with extra material. When you place this into the pressure pot, close it up and add pressure, the air forces the bubbles deep inside the mold to pop and the extra fluid is then drawn into the empty areas. I usually leave my castings in the pot for hours to make sure they fully harden before taking them out, but once they cure, then you will open up the molds and see that castings can be perfect or nearly perfect. The other thing that helps is realizing that you are trying to do something that traditionally is done with very large machines, and even in injection casting, there are still problems, what you face is not your problem alone. I almost lost faith about a year ago when casting Oblivion rifle parts, but it took stepping back and rethinking the issue. Eventually what helped was heating the molds, baby powder used on the surface to break surface tension, and pressure casting all the parts after injection. I still get air bubbles, but they are a lot less then they were when I started. I also changed silicones, I use sorta-clear platniums that are relatively more expensive, but I can SEE the urethane as i inject and I can see where air is trapped and make attempts to get the bubble out.
Long winded I may be, but I hope some of this helps. If you haven't already, search out pressure casting on you-tube and at smooth-on, they have tutorials that explain everything much better then I can. And as a last ditch effort, if you want to ship me a part, I will make a mold and cast some pieces to show you what I mean. I hope you don't give up and please keep at it, many of us here on the RPF are willing and able to help, just reach out to us.