"hardened and aged" is not necessarily a cause for issues. Also, the problem is rarely where the cables exit the coils, even when you may think it feels flimsy. So I'd start by simply clipping the cable ends 1-2 mm and firmly screw on the plugcaps again. But not before you have used the occasion to check the resistances. Each plugcap should have 5-7 kΩ and from one cable's end to the other you should have 13-15kΩ.