I purchased a stock Improved coil PN 4294 in March 2006.
I recently started experiencing poor ignition at Mid to high RPM range, after approx 10 mins of continuous operation.
I suspected the coil; as the symptom (from collected local opinion) usually leads to the coil.
After I removed the MSD coil and replaced it with a borrowed OEM unit the engine ran perfectly.

Does this mean that the MSD unit is now a throw away?
Is it possible this symptom is in fact just a break in the leads or plug clips?

As I live in Australia, to return the unit to USA for appraisal would be time consuming, so any info or conclusions you can draw from this fairly specific problem would help me to decide wether I return it to you or attempt to repair myself.
The MSD coil has a number, "C#538" on the side.