GMC Repair: Distributor cap problem, gmc savana, distributor caps

Question
I have a 2001 GMC Savana, 5.7 V-8. 8 months ago it all of a sudden sputtered badly and would not start again. I took it to a mechanic who said the distributor cap was badly corroded. It was replaced and the vehicle ran fine. Since then, about every 2 months the exact same thing keeps happening. I've taken the vehicle to 3 different repair shops and no one can figure out why the distributor caps keep corroding and burning out. Hopefully, you can help me. If not, then maybe I can buy distributor caps in bulk!  

Answer
There are NUMEROUS possible faults that can cause this fault, But I would need to see the cap and the exact location of this corrosion in order to make any possible suggestions as to what the cause is. I would need to see the COLOR of the corrosion and the location.

If you can e-mail me a COLOR photo of the cap then I can probably give you some items to test.

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