Was line still on the reel when he brought it to you? The reason I'm asking is because whatever damaged the spool would have to have damaged his line first.

No, not if the substance that corroded the reel wasn't corrosive to the line.

With "Dissimilar Materials" Galvanic corrosion does not require any moisture, salt, or corrosive substance to be present; all that is required is for "Dissimilar Materials" to touch. The galvanic corrosion is where it started, corrosion will always take the path of least resistance so the galvanic corrosion spread intergranular which means it separated the grains of the graphite which is why it was not noticed until a year later. The exterior plating/coating/finish held the graphite separation in check until the pressure of the separating graphite finally blistered the exterior finish and it cracked.

The path of least resistance on the spool was the surface of the spool which is why you see two different types of damage.

This does not rule out outside materials (worm salt) compounding the problem

whatever the cause, its the operators fault. Reels just don't do that by themselves...

whatever the cause, its the operators fault. Reels just don't do that by themselves...

And what do you have to back up this statement?

Fault? So if a tree falls on your car, its your fault for parking there? Not interested in finding fault, just cause.  :

Fault? So if a tree falls on your car, its your fault for parking there? Not interested in finding fault, just cause. :

I gave you the cause 

Yes, and thanks very much for all your helpful info, Catt.