Stuck Cylinder Stud

912ULS. Cyl #4 top right. Some years ago the cylinder head nuts were fitted incorrectly, with the sealed dome nuts on the top studs and the open nuts fitted inside the rocker cover. The engine leaks oil.  #4 top right dome nut is stuck to the stud.  There is approximately 3 to 4mm rotational movement but the threads (either end of the stud) are just not releasing. We cut the top off the dome nut to confirm that the stud moves with the nut. Penetrating oil has been tried and heating the nut had been tried. From the logbook, the nuts were torqued 3 years ago to 10Nm plus 180 degrees, not 120 degrees. Two nuts/studs were originally locked like this but I was able to free one of them. I believe the threaded insert inside the block is rotating.  Before sending the engine away to have the stud removed and have all 16 studs replaced.. I'm asking you chaps for a 2nd opinion or alternative suggestions.  The engine is in Caboolture. Thanks in advance.