Part of power IC is rusted

My MacBook started giving me issues while using (would automatically shut down etc etc). Took it to an authorised centre and they told me that my battery was loose and they fixed it. I started having the same issues again so I took it to another authorised centre and they told me that I had rust formation on one part of my Power IC Chip. They wanted to replace the whole mother board for close to $900.

I wanted to know where I could get the particular part and whether if I found it, replacing only that part would make my laptop work

PS. My laptop works but has to be plugged in all the time