Hello XXXXXX XXXXXXX,
The distributor cap and rotor are mounted to the Optispark Distributor under the water pump. The most likely cause of your concern is the distributor cap and rotor are crossfiring. If you haven't already done so, have the cap and rotor replaced. If the water pump shows signs of leaking, have that replaced at the same time because the pump needs to come off to get to the distributor.
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Russ
ASE Certified Technician
19 years of GM Dealership experience. ASE Master with L1 and GM Master Certified in Electrical