I found out why my injector looked leaky. When I open my bonnet after washing my car the bonnet drips on the injector. What makes it worse is that it drips before the bonnet is open wide enough to look in it. So when I open the bonnet (which is almost always after I wash the car) it's nice and wet there. I noticed today because the pipe just above the injector had a drip on it, and it could've only come from above.
So my injector probably isn't leaking. I don't know whether the water could get into it though and cause my problem? Or maybe the water could drip on to other things like the ignition leads? Don't worry, I know you don't want another massive thread. I just thought the info about the leaky injector would make you laugh.