My two cents as I recently replaced the two lines to the engine from the thermostat.
Nothing worked for me. I had good access to the thermostat via the lift in my garage. Heating, oil penetrant, soaking, hammering, nada.
This applies to all four sides.
Finally since I didn’t care about the oil lines, two hours later with a dremmel tool I cut out the line nuts diagonally and even with one third of the nuts these things were hard to remove.
I wish you better luck.
I did apply antiseaze for the next lucky guy.
