This is a good reference - thanks for the thread link.
I would add that there are four screws fixing the logic board to the baseplate. Three metal screws near the perimeter, and another NYLON screw nearer the centre. This functions to ensure good contact between those ICs under the logic board and the thermal conducting pads that link to the baseplate as heatsink. Over time, those pads shrink to fit the shape of the chip that is pressing down on them. So anything less than a good pressure from the screws, including the nylon screw, can mean a weak contact between chip and pad. If concerned about this, you can buy slabs of the thermal conductive pad material (make sure to get correct thickness) and cut them to shape to replace any that do not give a firm contact. Usually, the thermal paste will be sufficient.
Rick