Caliper problems 2004 Double Cab

Alright Yall so I've been having some issues with my brakes. All out of the blue they started squeaking roughly a week ago. Today I went and picked up that goo that you put on the back of the pads to keep them from squeaking.
Good news: no more squeak
Bad news: my upper left caliper piston would not compress when I tried to compress it to remove the brake pads. All the other 3 moved with slight force but nothing abnormal. The 4th one would not compress no matter how hard I tried squeezing it. I know I probably have to change the caliper but I'm hoping someone has some suggestions as to other causes. Also, since putting everything back together, my brake pedal has been a bit spongy. Still stops fine but the pedal requires more pressure than usual.

 

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