ss used his keyboard to write :
I have soaked in WD40 for a couple of days and still stuck.
The arrows in green are points I can tap with hammer but dare not hit too
hard in case the `lug` breaks off.

WD40 is next to useless as a penetrating oil, try a proper penetrating
oil or diesel.

Hot air gun may help a little, I would hot and cold shock, spraying
penetrating oil at the thread block interface so the cold contraction
helps draw the oil in.