Therma; pads on laptop GPU

I have an Asus laptop and I took it apart including the heatsink. The CPU is covered with thermal paste as expected, the graphics chip though is covered by a thin thermal pad similar to whats pictured below. I know of course that thermal PASTE must be cleaned and re-applied every time the heatsink is removed but what about the thermal pad? Does that also have to be replaced or can you leave it? It's not like pre-applied thermal paste the pad is kind of jelly like and solid.

The thing is how do you know what thickness to get and what kind to get. This isn't like pre-applied OEM pads that melt with heat. Like I said this one is kind of solid and jelly like and it keeps it's solidness even under heat. It's also the right thickness so it sits nicely between the graphics chip and heatsink. If you dont get the right thickness it won't sit right which won't help cooling.