mine done that, gotta make sure its on properly mate especially around the oil pump area i used red sealer in the end and it was fine, if its coming from that end.

A trick is to get sum mig welding wireand put it through the holes on the corner of gasket inside the gearbox part and through the holes in the block, then push the sump up onto the gasket put some of the bolts in then just cut the mig wire and pull it out!,

if its coming from the gearbox side, check its not your crank seal as it can drip down onto the sump