The optispark unit is the spark distribution unit for the engine. On previous Vetts, the standard HEI (High entisity ignition) system was used. However, for the LT1 the opti was positioned on the front of the engine driven by the cam gear. The problem come by nature of its opperation and location in the engine compartment. First it uses an optical trigger to distribute spark to the firing cylinders. Secondly, when that optical trigger gets wet, it no longer functions as it should....rough idle, no start condition etc. The location is the other problem. The water pump is also on the front of the engine. Actually the opti spark is just behind the water pump (looking at the front of the engine) so naturally, any coolant leak with render the opti spark wet.