Phone change from i337M to 9505

the complete story...

i purchased a new samsung galaxy s4 GT-9505 international unlocked, (it came from Rusia) and it had not the band for 4g in USA. 15 days later I just crash the screen and i took it to repair, but in the repair store they got some problems getting the new screen and they put one from another model, i receive once the phone and the touch buttons (to the left and the rigth of the home) were not working, i returned it to the repair store and after a month or more i got my phone back, but it has been flash with a Mexico (claro) firmaware, (AP I337MUMUEMK6) the only good thing is that the 4g was working. it has a problem that suddenly the wifi shutdown and you need to reboot it to enable it again, it became more often until now that it's completely death (the Bluetooth too), reading in the forums i found that it may be a problem of the firmware, so i flashed it with the version I337MVLUFNC1, and it worked just fine, including wifi and bluetooth, but after a couple of weeks i got the same problem, wifi shutdown with the Bluetooth and now is not working at all even if i flash it again, i tried using several rooms such cyanogen but i think it's not the problem. i'm not an expert in android devices, i don't understand where the drivers are, i guess that in the ap file. i know that the broadcome card that manage the wifi/BT is integrated in the main board of the phone, so i'm not sure if it could be a hardware issue, i think is related to software/drivers
what i'm traying to do now is to revert my phone back to the original version GT-9505 to see if it fix the problem, i got the samsung offical version (the 4 packages AP, BL, CSC and CP, but when i want to flash i got an error while trying to "re-partition" , so i download the "re-partition" table (pit file)for the GT 9505 form here, in one post, but before do this i want to come to you to get your advice, is it something i can do? or is there any other and better way to try to fix it?
in the other hand, if i got to work the 4g after the several week of repair, it mean that they finally change the main board too? basically, they change internally all the phone?
please advice.