Remove thermal paste.
Original thermal pads do not require it.

If you keep the white thermal paste on top of the thermal pad of this console and turn on the console once a year for 1 hour, will it cause a lot of heating and reduce the lifespan of the chip because of the white paste? How many degrees does the white paste increase if it is on top of the thermal pad?

Best way is to replace thermal pad for new as they have some life span but not 25years, possibly someone b4u split it open ant thought its a good idea.

Question termal pate in PS2 Slim 90000
 

I got a PS2 Slim 90000. When I opened it, I saw that there was a bit of white thermal paste above the thermal pad of the EE/GS chip. The paste is in contact with the heatsink metal. This paste is not original from Sony. Will it cause the console to heat up, reducing the lifespan of the components? Or can the white thermal paste transfer the heat from the thermal pad to the metal?
Is it necessary to open the console, disassemble it, and remove the white paste?