Controller Inputs on all 4 players with working controller.
Reading / Saving to working memory card on both ports.
Run a game for 30 minutes. Let those caps warm up
Completely disassemble the console. Every screw, sprint, including the controller port, lid and fan assembly.
Pull all the plastic pieces out and gently wash them.
(Optional) Retrobrite any pieces that have faded that you’d like to try to bring back to life. NOTE: Some Gamecube ABS is already pretty brittle. You risk turning the plastic to crumbles, or discoloring instead of fixing. Be very moderate. Likely obvious but stating the Platinum is just paint!
On the Motherboard, carefully remove the Heatsink. You make need to power on the console to warm everything up if it is giving you a hard time. Don’t violently force it off. Remove the Thermal Pad and throw them out. Clean the chips and heatsink with alcohol and a quetip.
Use compressed/accelerated air to remove dust. Give everything a good brushing on the Motherboard, controller pcb, and power supply if this is a DOL-001.
(Optional) evaluate if you need to give the PCs a Ultrasonic bath. If they are pretty grimmy, it may be worth the effort.