RyanSoundLab
Trade: Ryan Sound Lab
The relay on the 525 has a single coil and two sets of contacts. Since it switches one channel OK, the coil system is working. It's just bad contacts on one channel inside the relay and there's nothing you can do except replace the relay. A suitable replacement looks like Littlefuse # HE722A1200 or try to find a used 525 on ebay?