[BruceinLA]

The brake fluid should be flushed every 2-3 years, that kind of damage looks like a petroleum product got in contact with the rubber.. in any case it's time to flush out the brake system.

 

[BruceinLA]

Are you in a rust belt state? Corrosion would be a more likely cause to lock up a caliper. See if it moves freely on the sliders or if the piston is frozen (as in you can't squeeze the piston in at all)... Just something we don't see in Southern California, I don't have experience with "locked up" calipers of any kind here.

In any case it sounds like you need to replace that caliper and flush out the entire brake system.

I've refused to work on a few cars because of excessive corrosion, Sometimes the rust is just too much!