Sadly the bottom side of the logic board which if you take off the bottom cover then is often not the first place the liquids gets into. You’ll need to take the logic board fully out to inspect the other side. Review Steps 3 & 4 in this [guide|123653] the second picture in either is the other side.
It maybe time to find a Mac repair specialist near you who haves the deeper skills and tools to repair/replace the needed parts.