Because as it stands, your said your console is still running hot.
Prolonged use of a abnormally hot console will only lead to damage.

If you've ran the console hot for a lengthy amount of time, chances are you've damaged the solder between the CPU/GPU. No amount of thermal paste will cure that.
Even the oven method is only a temporary fix.

The way I see it, you have 2 options..

1. Repair all possible damage internally (reball and thermal paste). Add extra methods for keeping the console cool. Ventilation/fan mods/console elevation.

2. Look into getting another console.

If you don't want to risk making your console worse, then you've got to assume it needs internal repair, then prevent it happening again in time.

Of course, you seem adamant on only replacing the thermal paste, so I wish you luck with your temperature issues dude.

We'll see tomorrow. I mean I don't really care about the playstation, I could as well use it for spare parts or a door stop. I got plenty

What console is it? I have a Phat PS3 that I changed the thermal paste on yesterday. I also did a case mod to increase the airflow/hot air escaping.

Simply drilled a circle of holes the circumference of a large glass (all the way to the core of the circle). Added 2 inch rubber feet to the 4 corners of the console.

Prior to this, the console would cough out hot air and the fan was always in overdrive. Now, it's cool even after hours of use. You can take it further and add extra fans but I don't think that's always necessary if you are careful with the console.

Keep it stored in a well ventilated area free of dust. And raise with something in the corners.
All pretty self explanatory stuff but helps prevent the YLOD.

Seeing as you already had this. Try the oven method, it does work but isn't a permanent fix. Reballing is the only real fix, then prevention methods from there.

Hope your PS3 recovers .

After applying new thermal paste my CPU now runs at 65C. Problem solved if you ask me, i will however make that hole