I have never had any problems with fuel tank , there is no corrosion and up until now it has never leaked , this week I overfilled it to the point that you could literally see fuel in the filler neck , I went back to the house and when I returned the level had gone down however it was now on the road and dripping from top of fuel tank , it eventually stopped and had actually lost a very small amount of fuel , is this a contingency for over filling or do I have a leak high up in the tank ?

Check the vent tube and filler tube are correctly fitted , my seal on pickup pipe some times leaks.

Also check/replace the gasket on the fuel sender. Could also be marginal fuel filler pipe between the side of the box and the top of the tank, or the vent hose. These do perish after a while and will do what you describe.

Take the plate off the top of the tank and overfill it again - you'll see where it is leaking.

I replaced my tank and had the same issue. It was leaking where the filler pipe fastens over the tank filler spout. A 2nd jubilee clip sorted it.