I'll add my two pence, I've found that the corner petrol station has been adding ethanol to the petrol, and I think it is in higher amounts than the stated 10%. The results on my bike is that the plastic in both the fuel line and filters becomes brittle and is prone to cracking. It also seems to dissolve the gaskets at the fuel tap/tank joint. It also seems to dissolve the inside of the Indian fuel tap.
On a related note, in the past I would fix seeps like this with the bar soap method that Mike Baird suggests. However, I have found now that the ethanol has been added to the fuel, the bar soap method isn't working for me. The ethanol dissolves the bar soap gel fairly quickly.
My recommendation is to replace the fuel line, gaskets etc. with some sort of rubber that resists ethanol. Then see if you can find a petrol supplier that supples petrol without the ethanol.