I like Q8 would check the fuel hose clamps. If they are the factory crimped clamps they may be leaking intermittently. I had evidence of fuel on the aero screen but since adding proper screw fuel hose clamps all clear. Cheaper worm drive (jubilee) clamps are not up to the job as they do no tighten evenly round the hose. Not got the car at home but if I remember correctly there is a cross over pipe between both inlets so you need 6 clamps.
Tim
