Failing resistors in mid 70's Sansui gear

A good friend owns a shop in Austin. He has some interesting info on mid 70's Sansui gear. As a Sansui fan, I thought I would share this.
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Started with Sansui reciver that i got in Viet Nam.
Those look like carbon film resistors in the photo.

If carbon films or carbon composition resistor get heat during normal operation, they will slowly decrease in value. For this reason they have to be run at values substantially less than their ratings- no more than 20% dissipation!