Gti gravity valve

I'm making a bit of an assumption here, and this was a problem last summer as well which I still haven't had a chance to look at..

So I filled up the car this morning, half forgetting that the car dribbled fuel out of the trumpet vent when the tank is full and particularly in hot weather.

When I left work I went to halfrauds, then to the hospital for an appointment which all in about 4 miles, when I got to the hospital I got a whiff of fuel so I looked under the car and its dribbling like before, so I decided to release the pressure by taking the filler cap off (bad decision) it literally spat possibly half a litre of petrol out all up my arm all over the side of the car, made a right mess. The force when I turned the cap was quite something.

So my assumption would be that my gravity valve is goosed, but being that they are hard to come by, has anyone had any success cleaning them out if so what with? Brake cleaner or something?

Is it dangerous to drive with that much pressure build up?

 Would a vented filler cap be a solution, or would that mess up the way the gti fuel system works?

Cheers, karlos.