If you still have the single piston, it gets a little siezy over time too. Ive had to pull mine all apart and rebuild it recently. If the brake is not feeling like its applying very hard and also doesnt seem to back off of the disk very well. Like you can feel or hear it still grinding on the rotor, you may need to do the rebuild.
A kit like this...
https://www.amazon.com/gp/product/B07C8KV4N1/ref=ppx_yo_dt_b_search_asin_titl...The piston gets junk built up around it and may even have some rust keeping it from moving back and forth freely.
Just somethign to consider.