Small amount of corrosion on the bolt and it becomes almost impossible to remove. Alternator out to change the diode pack. The stupid corrosion added a good hour to the job. lots of wd40 a taps with the hammer. Unfortunately the space in the engine bay means you can only get a 2 inch swing on the hammer. Lots of taps, + lots of wd40. tapping in and out again until it came free. a good clean and plenty of copper grease when I re-install it.
My car lives inside. Left longer, this bolt would be a total mare!