In related news, thoroughly cleaning the dust out of and reapplying fresh thermal paste to a twelve-year-old CPU and stock Intel heatsink made a
huge difference. Most of the case wasn't even all that dusty. A very fine powder in some areas, but no chunky dust bunnies.The case intake filters were a little dirty but not terrible. In the heatsink itself, though, I could see many of the gaps between fins were pretty clogged along the top where the fan connects.
In that screenshot I posted before cleaning, the CPU was reporting 53°C when mostly idle.
After the deep clean? It reports 38°C when mostly idle.