Repaste after removing the heatsink. Always.

Yes. Even if your temperatures look fine right after reassembly, you should still repaste.

Thermal paste isn’t designed to be pulled apart and put back together. When you separate the heatsink from the CPU/GPU, you introduce air gaps and uneven coverage. The paste that was perfectly spread is now a mess — some spots will be too thick, others too thin, and some will have bubbles. That works fine for the first few boots, but as the system heats up and cools down, those weak spots cause hotspots and gradually worse temps.

I know the temptation: “It’s booting fine, temps are 40°C idle, let’s just close it up.” I’ve done that. Regretted it a month later when the laptop started thermal throttling under load. A tube of decent paste costs maybe $8. The time to clean and reapply is ten minutes. Skipping it is false economy.

A soldered RAM upgrade is already a high-stakes job. Don’t cheap out on the last step.