Ipod Touch 2nd Generation

The Ipod was taken to a service center in Colombia (MacStation) in which the following reply:

BE RESTORED AND THE IPOD WORKS WELL DURING A TIME TO BRING BACK THEN RANDOM FAILURE ON THE SCREEN DURING INSPECTION PHYSICAL CHECK THAT THIS POWER CONNECTOR SULFATE This only occurs when liquid gets SHOULD TALK TO THE CLIENT FOR THIS AND THAT REASON NOT GUARANTEE PROCESSES.

I can assure that the device has not been wet because the moisture indicator used in the headphone jack does not have any change.

The service center suggested to me about USD $ 90 for an exchange for one with the same characteristics, which does not seem right.

My question is whether the fact that the plug this "sulfated" invalidates the warranty.

What should I do?

Thanks