I see no reason to replace the whole distributor
* If the rotor button is missing, I would replace the cap & rotor
* If the button is still there, I would instead clean the cap & rotor in the kitchen sink with dish soap & water, then let dry overnight


Also, check the timing so you can see if it is correct. No tools are required to check this. If it's too far advanced, the engine won't be able to rev very high under load


Vacuum is not the what rallywit was talking about. He said:
Quote:If either screw is missing it will cause highly erratic spark timing

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