Well,

I always thought my car went through fuel like it had a hole in the tank.

If the car is left for a few hours, you can slightly smell fuel in the car. Just noticed it now when the car was filled to the full mark, generally it sits around halfway.

Fuel filler cap is fine, seal is perfect.

Have not had a chance to check the fuel lines at the top of the tank (this friday my mechanic is doing the suspension/brakes - so I'll have a chance then).

Bottom passenger side of the fuel tank is wet, not greatly, but enough. Almost looks like its coming from the join mark - but cant drop the tank as its full, so dont know if its a leaking fuel line from the top of the tank, or if its the tank thats busted.

Now - worst case scenario - anyone know what a new tank goes for?

Yes I've dropped fuel tanks before, dont really want to do it either - but I dont want to be burnt to a crisp too.