If the pads are coming out one side only you've probably got a sticky piston.
Apparently a drop or 2 of mineral oil on the piston and gently work them in and out and that can solve the issue.
One of the only brake problems I've was the lever being slow to release very rarely.
Only affected the front wheel so a quick pad removal and gentle de-dusting with a small paintbrush fixed it. Front caliper picks up more dust so the rear is still fine.
I didn't want to hit it with anything sticky that could hold more dust. It is that real fine powdery stuff that seems to be the problem and I didn't want it blow it in further with a compressor.
My rotors also needed a bit more space towards the outside of the caliper to centre it all. A few 1mm stainless steel washer fixed it. Never worried about it since.
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