galaxy s3 not charging

I am in the process of trying to repair a water damaged S3.

When i received it, it was completely unresponsive, although owner had said if he put already charged battery into phone it powered up.

I spot cleaned the charging port and some other damage i could see and eventually got it to charge.

Great, or so i thought.....

I gave the phone back thinking all was well but it has came back to me, as was not recognising sim. I removed sim tray assembly and cleaned underneath it with no success. I then ordered new sim tray and put it out of my mind.

When new sim tray arrived, I went to power it up and nothing happened. Tried to charge it and laptop never recognised anything connected, changed cable in case it was faulty and then checked new cable on s3 mini I had and it worked on that.

I then gave motherboard a bath in 99% isopropanol (twice) and still nothing.

The only damage i can still see is to gold parts of motherboard (kind of a figure of 8 shape) and I'm wondering if this could be problem? Can this be re-soldered or should I be looking elsewhere on motherboard.

p.s. Phone starts up if I put charged battery in it and I can put pictures up of damage if that helps?

Any help GREATLY appreciated!!