Been there. My money is on the sump. I've got mine sorted after countless attempts and tried EVERYTHING. What worked for me was PAYEN gasket - Kimbers locally supply them. No glue, silicon or anything. Fitted gasket to cleaned sump surface and offer up to cleaned block. Worked center out with a 1/4" drive ratchet nipping up then repeated tightening just a bit more. Iirc the manual says 5-8nm but when I torqued up like this it pissed out. Good luck.