CHECHC04 maintenance advice

Well I finally found and bought PS3 CECHC, Did a stress test ( the last of us and GTA 5 ) before buying and checked everything and it's still sealed.

Should I break the seal so I can open it and clean it up ? Also to change the thermal paste and change the bios battery or how should I call it because it's dead. Or should I clean it only from the outside ?

Checked the runtime which is not that much to be honest and syscon error codes. Interestingly enough there is an error code which hints that it prob had a YLOD but it works now ? So I don't know to be honest. ( Dates on some errors are not correct because bios battery is dead )