Well I have dropped the tank and replaced the rotted rubber hose that connects onto the sender unit so the leak problem is solved.........BUT i have a question for you. When i had the leak from the tank the leak was intermittent it happened often but not always. I live in the very hilly town of Hastings and it leaked both on level ground and and on an incline. The final straw was when it was leaking parked outside my house facing downhill on a slope of ( i think) about 30 degrees. The tank was about 20% full so on the slope petrol would not have been high enough to overspill out. Also liquids do not flow up hill, so why and how was there a leak? Was there a pressure difference between the carb and the tank causing petrol to be sucked back into the tank and leak at the rotted rubber connecting hose? I find this very puzzling and interesting does anyone have any answers cos it doesn't make sense to me>

wasnt it that the petrol was sitting in the well on the top of the tank and when tipped forward and to the NS it ran out the cut out for the pipe and electrics?

Hardy, liquids are weird things and can sometimes behave in ways we wouldn't expect - although there are always valid reasons for their behaviour, of course. I guess a possible reason for your symptoms could be temperature changes - when the petrol tank warms up in this fine weather, pressure will build up in the tank. Normally this pressure will either be expelled via the filler cap, or else will just be contained within the tank and lines - but it could be enough to cause your perished hose to leak when stationary.

Or, as Sean says, there could be a tiny leak all the time when driving and this could 'pool' on the top outer surface of the tank. As soon as you stop, it'll trickle off depending on how you're parked.