I think you were correct mate.   I replaced bank 2 gasket between manifold and cat. The old one was completely burnt through on one side.   Have done several journeys, few hundred miles, and the stalling problem has gone away. No EML and idle is normal. The P1283 had not returned.   Pending P1273 on bank 1 but I didn't have time to do that gasket - once I have I think this will be fully resolved.   Cheers!