hello there mate i done my sump gasket 4 times and it was still leaking from the same area as yours ,now it might sound funny but this does work as i found out on the 5th time .
take the sump of and clean it well specially at the top , now for the funny bit,
on the edges of the sump and where it bends super glue the gasket on, not too much glue just enough to hold it in place ,then clean the surface on the bottom end
where the sump goes, and fit the sump on tighten the bolts from the front of the sump all the way along to the other side but dont overtighten it . hopefully this should do the trick. good luck
mine never leaked after that.