The TP is not going to melt away and onto your logic board, but eventually will need to be replaced. Usually that equals the life of your computer, unless you take it apart/break the seal in which you will need to apply a new layer.But would the thermal paste thickness stay constant in time, or will it get thinner/diffused away? I mean would a 1mm thick layer of thermal paste remain 1 mm thick 6/12 months later (of course, I know the concept of conservation of mass, but just curious if there might happen any kind of melting etc.)