Ps4 over heating

I got a PS4 that was overheating and having disc drive issues, got the disc drive resolved. There was a decent amount of rust on the motherboard metal plates and heat sink, looked like moisture from humidity and not straight up liquid spill damage because the board is fine. I deep cleaned the system and unplugged the heat sink and replaced the pads and paste, and still got the over heating message and the fan screaming but only when booting a game, so I tried a spare set of metal plates with no rust. This seemed to help because I played a game for about 30 minutes no issues, turned off turned back on, loaded the same game, fan screaming and starts to over heat but I caught it and quit the game and it calmed down slowly. I have a replacement fan on the way today but I’m not sure that’s gonna fix it because the fan seems fine. Any suggestions?