So I pulled it out after 24 hours soaking. The two dowel pins punched out very easily, so the home brew was definitely effective for that job. But the cast iron back cover still won't budge, after repeated blows all round the perimeter with the BFH. I tried inserting a thin blade at the joint with the cast aluminum, and after a few light hammer taps, all I succeeded in doing was rounding off the edge of the cast iron cover......no separation, no gap. It felt like I was going to break something if I continued, so back in the home brew it goes overnight. I guess the factory didn't use a gasket.....Patience and perseverance being summoned.