its NOT the head gasket. the crankcase and the transmission case are separate. the only way for water to get into your crankcase from the cylinders is for the head gasket to be leaking, and the right side crank seal to be leaking. the antifreeze would have to get down below the piston for this to happen. i dont see that happening, so i think you can rule out that. water jacket?? thats in the cylinder and would have nothing to do with this. so rule that out. have you checked the water pump seal where your impeller is? im betting thats where your problem is...
as for your overflow bottle.. take it off and throw it in the trash. its worthless. its definitely not gonna stay full if youre leaking coolant into the crankcase.