Is replacing thermal pads useful for maintenance?

[datadestroyer]

Are there any risks?

I've tried searching around, but I don't see many people talk about this. Is it because it doesn't affect much? I would've thought 20 year old thermal pads would be losing their effectiveness by now.

If I do want to replace them is there anything I should be looking for (ex. thickness)?

 

[sandungas]

Yeah, is a good practise, sony was using different types of thermal pads along the PS3 production, some are darkgrey, others lightgrey, and even some blue ones too, the exact composition of each could be different, i dont really know, but some of them had some kind of "oil" (feel wet to the touch)... this kind of thing gets dry with the time, and the material gets deformed too (doesnt returns to his original volume)
If you see the thermal pads have permanent marks with the shape of the component they was touching, and are dry and rigid it means that are bad... they needs to have the feeling of a bubblegum

Most people recommends to use thermal pads with a thickness of 1.5mm (and are going to be pressed down to 1.2mm or whatever)
But you can stack them too... lets say... if you want to place a thermal pad in another point of the motherboard where there is a gap of 2mm you can use 2 thermal pads of 1.5mm on top of each other (total 3mm)