If it was solvent softened cellulose, which was comon, yes, it will turn into something resembling cracked glass ....
No idea what the spline tool fits, but I have an ignition wrench set that also has a stamped wrench with a spline cutout in it, so there is something out there, somewhere, with a spline screw on it....
(Probably to keep joe homeowner from letting the springs escape from his magneto...;P)