As ever your advice seems good-double checked the cranks by marking on the axle with a end with a pen to see which crank was loose, and it was indeed the drive side Not the non drive side as I originally thought, despite how it felt. Tightened that cotter pin with a little sharp hammering and so far 20 odd miles riding with no issue. Will give the cotter another shap hammer today and hopefully it will all bed in and hold with no further loosening
As ever your advice seems good-double checked the cranks by marking on the axle with a end with a pen to see which crank was loose, and it was indeed the drive side Not the non drive side as I originally thought, despite how it felt. Tightened that cotter pin with a little sharp hammering and so far 20 odd miles riding with no issue. Will give the cotter another shap hammer today and hopefully it will all bed in and hold with no further loosening