@JoG, I have a torque wrench, and I made a ghetto breaker bar with a piece of 1x2 see photo below. Washer does appear to have a sort of flattened edge.
OK some good news and some bad news...
Braced the bike up to a wall, chocked the rear wheel with a brick got the gf to sit on the bike with the brake on and ... it actually was pretty easy to get off. That's the good news. Er...it's also the bad news. I couldn't feel any play in the pulley when it was attached but it wasn't held on with much torque
When I check the play on the pulley *without* the bolt it does appear to have a bit of sideways movement, maybe a sixteenth of an inch, forward to back is better only very slight maybe a half a millimetre.
I made a video too to show the movement
https://youtu.be/thoaDkeCaF0The photos below appear to show the splines in good condition, but then I'm not certain what they are meant to look like. This movement appears to be a bit of a concern but again I'm not sure if that is normal when the bolt is not attached.
Got some loctite blue but not sure if I should put any lube on the splines, I have some hi temp bearing grease.