@swanny21445 "is it possible for a well educated technician to do it", Yes. "retain some level of water tight seal" Maybe.
The very first area that you want to check, are your antenna cables. Those connect to the sub_board (daughterboard) Make sure they are all seated right and that there is no crack on that board. I Personally would even consider replacing it. Then check the flex cables from the daughterboard to the Main board. Check for tears and cracks in the connector etc. After that you are looking at a board issue.
Since iFixit does not yet have a guide for this, use something like this video or use the guide from here It is written in Spanish so make sure that your browser can translate it for you. Replacement daughter boards are readily available at many online stores.
While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has a device with the same issues as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.
Repair is War on Entropy!
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