Intermittent battery drain

Hi. So my wife bought a 2013 Kuga 4x4 gasoline. Had it for about a month without a problem, then one morning the battery was dead. Bought a new battery,but next day dead too. I noticed that sometimes we could lock the car with the keyfob but often the locking did not work. Nothing would happen when we pushed lock, but the open button always would work.

I then noticed that when the car wouldn't lock, the info display between the clusters would not turn off. It would always stay on. And when snowing outside, the windshield would have a round spot where the snow would melt. 

We took it to Ford, but ofc the problem was gone when they had it,they couldn't see any parasitic draw, but they did check the door lock and saw that there were corrosion on the right front door as this was a known problem area for parasitic draw. They did change the wireharness and antenna in the door. 

We got back the car and it worked that day,but next day the lock did not work again and display is on... The mechanic told me that if this does not work,they have to cut open the harness and check wires more closely and this could take some time and ofc money.

Have any of you guys had this problem? Maybe some tips to where to look. I was thinking of troubleshooting myself before driving it to Ford again, to save some money.