I've just had a distributor shaft seize solid in it's bushing, basically locking the unit and twisting it around untill it's rotation was stopped when the vacuum advance jammed up against the head. Both the cap and rotor were broken, and when I cranked the engine over the distributor shaft did not turn. .Upon further inspection, looks like the shear pin holding the driven gear to the bottom of the shaft was sheared off. Is there any chance that damage could have been done to the gear on the cam, as it appears to be machined into the cam itself and nor a separate piece that could be forced loose. Thanks : Bruce