Water ingress nearside rear footwell. HELP.

[twincampolo]

Water has been getting into my car ever since the heavy rain started back in november. It seems to only come into my nearside REAR footwell, the front is bone dry. It would seem that there are several problems that can cause this, window slot seal (replaced), scuttle panel drainage holes (cleaned), inner door membrane (repaired and re sealed). After heavy rain last night yet again my car is damp in the rear footwell. I have heard now that this can be a leaky pollen filter. All my symptoms seem to add up, but i cant find anywhere the actual FIX for this problem, as i dont see how removing my filter and putting it back in will help? can anyone detail what i have to do to stop water coming in, exactly how the leak occurs and why the hell its in my rear footwell and not my front one?

Thanks in advance, Im sure anyone who has suffered with water ingress problems knows what its like haha