If there is only leaks, the shaft seal in my case for example, it could be fixed by repalceing seals and O-rings. But if there is damage inside the compressor, on cylinders for example, you need replace the damaged parts and the whole systems should be cleaned and flushed. My case is relatively simply, it was just the shaft seal leaking. I bought a gasket kit and a shaft seal kit, and problem has been fixed.