Saving Old Seagulls

i have a few flywheel keys and none of them seems to want to stay in the hole in the crankshaft. l have previously removed and replaced others with no problem and so i was wondering if there was a trick i was missing somehow that i had not needed before.do crankshafts have their own key that is matched to fit them( like the thrust washers on the prop shaft) or should any key be able to fit? woud appreciate any advice.

A blob of grease helps.

thanks hugz. will try that later today. frustrating though as i have a rebuilt century ready to go but for that tiny piece of metal!

problem sorted. l just had to slightly grind one of the keys into a better shape to make it a tight fit.