My 959 runs pretty warm during extended transmissions on the left back and the left rear side of the radio. It's still set at 4 watts am dead key and 12 watts SSB power with the 2018 mic cranked all the way up as well as the radio's mic gain. I've been thinking about installing a heatsink opn it or at least mount a fan on the back to blow on the radio.
A single heatsink with a small fan will suffice . . .