Honeywell PTM 7950, Thermal Grizzly Kyrosheet, DOWSIL TC-5888, Polartherm X10, or maybe Thermal Grizzly Duronaught for the GPU core. A lot of otherwise well performing TIMs aren't durable enough to last without hotspot deltas creeping up as time goes on.
I would always replace the pads on the power stages, but unless the GDDR6X pads are obviously damaged, or this is a model with unusually bad memory cooling, I wouldn't bother replacing the pads on the memory. The RTX 4090 doesn't benefit much from extra memory cooling.