Thank you for the replies! I'll change out the TIM on the Northbridge and Southbridge here soon. I'm pretty sure I had already done this on my Northwood Pentium 4 build, I think it's those horrid old yellowish thermal pad(?) things, but thermal paste still works as the heatsinks pretty much make direct contact with the chips in the first place. To be honest I was just asking because it's sort of a PITA to clean that crap off (mainly the heatsinks, hardly anything stays on the dies of the chipset in my experience), and I didn't know if it would still work okay or not after almost 20 years.
Couldn't be as bad when as when I bought a Radeon 9500 Pro without a fan recently and whatever gunk they used was stuck on both the die and was almost impossible to remove from the die itself. Had to also remove that stupid shim they put on there (that is taller than the die itself by the way!) for some unknown reason to use my own cooler because I didn't have a fan to fit the original heatsink and I had heard about issues with them not being lapped properly. Somehow through struggling to remove that nasty crap off the die and removing the shim I didn't kill the card and it works fine.