I have a spare Shift knob from a '78 Alfetta Coupe and was wondering whether it was interchangeable with the knob for the Spider of the same year. It looks the same as the original shift knobs I have seen (I have an ugly replacement), but the rubber gasket at the bottom on the knob seems to be too narrow to fit on. Are they not interchangeable, or am I missing something when I try to install it (I have been trying to push and twist it on, but to no avail).