iMac 4k 21.5" residue on motherboard. Dangerous?

[lainvoo]

Hello!

I started to disassemble my iMac 4K 21.5" to add more RAM and SSD. Right when I removed the display I discovered that the motherboard had strange residue mark on it next to the CPU. See attachec photos. The computer is working just fine. I would like to know if this is dangerous to the motherboard/computer?

I could assemble the computer as it was and take it to Apple, but what should I mark as a reason for them to open the computer and check the motherboard?

Or should I try to clean this?

Open to suggestions.

 

[TwoH]

Pretty normal to see, especially on iMacs from the vast amount I've done. I do like to remove it with a toothbrush to make it look cleaner though.

 

[lainvoo]

Thanks TwoH for this information. I thought this might mean that the moterboard/iMac will soon be toast.