Problem with 2004 BMW X5 remote keys

[Momus]

First of all - Hi! I've been a reader here for a while, but only recently registered to post some questions. Originally it was to ask for help with the dreaded timing chain cover weep hole coolant leak, but I was able to fix that using the bimmerfix stent, so now I'm moving on to the other (many) problems.

So, first problem... Both of my keys no longer work for remotely locking/unlocking or opening the tailgate. The interior central locking button works, and the interior tailgate release works, but the keys do not. They worked fine for several years, but first one, then the other began only working sporadically, and then each stopped working completely. There were several months separating when each key stopped working.

I have attempted to reprogram both keys multiple times, using the steps outlined here and other places. The first time I was able to successfully get them working again, but after a few months they stopped working again. Now when I attempt to program them nothing seems to happen.

Both keys do still start the vehicle, and will unlock the drivers door using the keyhole.

I have tested the key batteries with a multimeter and they are within the normal range.

I have also taken the keys apart and tried pressing the buttons directly on the circuit board.

Has anyone experienced something similar? Any advice on where to look for a potential cause?