Hi. I doubt you can get it repaired elsewhere but it worth thinking about the problem.
If the core module has the water sensitive markers showing ingress then Fairphone or more properly their goto repair centre Cordon with not attempt a repair, as it is will require a new main board.
Given the modularity issue dampness can get in, so being in pockets in rainy weather, or sealed pockets in the summer so the phone can’t breath ~ leaving on shelf in the kitchen etc.
Sadly you didn’t maybe ask for help before you sent it.
Here’s a topic/post about the water markers.
Read more in that topic and search for more such issues to get an idea of the problem you face.
I will also be in Bristol on 14th so could meet up.
However I don’t hold out much hope, it’s not like I have a spare core/main module. Main modules are the registered IMEI part of the phone that your call number is registered to.