What exactly do you need to replace between the chip and heat sink? Could you clarify? Also what are the symptoms of the STK going sour? Thanks!
As for most output devices, the STK modules are mounted to a heatsink to dissipate their heat. A thermal paste is put in between in order to increase the surface exchanging heat from device to heatsink (and therefore to obtain maximum heat transfer rate). The thermal paste is NOT there to conduct the heat from device to heatsink, as many folks think; the thermal paste is in fact an insulator, and shall therefore be kept as thin as possible.
If the metallic backside of a device needs to be electrically isolated from the heatsink, then a mica washer, with or without thermal paste, is inserted in between the two (not often the case for the STK modules I think).
An alternative that arrived on the market after these STR series is the SIL pad technology (combination of thermal paste and isolating function), but I haven't seen SIL pads for STK modules, only for regular transistors (TO-3, TO-220, etc). And it takes some knowledge to select to 'right' one as they come with different characteristics.
The remark I made is to clean and replace the thermal paste because it dries out, becoming more and more a thermal insulator (and reduced heat transfer surface) and the STK module becomes ever warmer, degrading the integrity of STK module, eventually resulting in failure. Hence, stressing (high volume) a vintage STK-containing amp/receiver can be risky.
PS: your avatar suggest this would be usefull for you....
Symptoms of an STK going sour? Well, when the sounds start sounding s**t
Meaning: too late :tears: