But rock it does. Northbridge heatsinks are designed for chips with large packages and/or integrated heat spreaders, more like 25mm square than 8mm square. With that much area, a 2-point mount is okay because there's no leverage to rock it. A small chip in the middle might as well be a single point fulcrum. It's super easy to upset.

We're already designing an improved heatsink (more dissipative surface area on the fins) with 4-point M3 screw mounting, like what's been working on our stickminers for most of the last decade. Might have samples in the next week.

Phil, I think yours went out before I started lapping the heatsink underside. The ones we got in were not exactly smooth either, and the smoother and flatter the mating surface, the better.