If you do go down that road (diesel), turn it over by hand, not on the button, or hello bent rod! If you ever do get it off, a good tip on here a few years ago was; before fitting barrels/head was, get all the studs nice and clean, cut lengths of heat shrink tubing, fit to studs leaving thread free, and shrink it. Stops the corrosion problem in its track! Still as valid now, as then!