I received the new power amps yesterday, and replaced this one just now.
(Yesterday morning i followed the audio signal all the way to the power amp, so it should be the power amp.)

I also added a heatsink so that the new power amp may hopefully live longer.

Tested again, and the sound is back. 🙂
(There are some minor crackling noices though, so i’ll have to check/replace the caps in the audio path.)