Pioneer SX-737 Distortion After 20 mins

I'm looking at this Pioner SX-737 which has distortion on one channel, the distortion starts after 20 minutes of playing.

The only other thing to mention is that this sandcast resistor becomes incredibly hot after only 2 to 3 minutes, so hot that I can't hold my finger on it.

Any ideas guys? Thank you!
 
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