Disco 2 how to remove worn ACE filter cap

Hi! I have tried to loose my disco. ACE filter cap using penetrating oil, screw grab and torch heat, but it begins to slip and the rusted cap is a bit rounded out. I should have replaced the cap when I replaced the filter five years back. Any suggestions to remove the stubborn guy are appreciated greatly.

Best advice I was given when I come to change mine was 'Leave it alone' !
Sorry not much help but it appears to have been good advise ?

Buy an Ebay block and hose convert, then swap the lot