Housing Change Help

Hello,

I dropped my Z10 and today I have my replacement LCD, middle plate and battery door, OEM. I bought the battery door just for the looks and my middle plate had a small dent. Also, I made the right decision because now the last screw holding my middle plate and LCD (the broken one), is stripped and so I cannot remove the LCD from the middle plate.

Anyway, I just wanted to ask what is this in the picture below? Is it thermal paste? I managed to get my fingerprints on it by touching it. Also, do I need to transfer it onto my new middle plate? By middle plate I mean the white part, by the way. Can I run fine without it or do I have to apply thermal paste or something? Thank you in advance.

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