Troubleshooting filament sensor problem  

Troubleshooting filament sensor problem

I have a MK2.5 that I originally purchased as an MK2 in 2016, then later upgraded to MK2/S and then MK2.5 in 2018. It sat and gathered dust for a few years during the pandemic, but I've gotten it tuned up and working again, and it's able to print fine, etc.

Except for the filament sensor, which doesn't seem to work at all now. I'm having trouble diagnosing what the cause is because I'm having a hard time finding any documentation on the MK2.5: everything I can find is on the MK2.5S or S+, which has a different infrared filament sensor. I can't even find a RAMBO connection diagram to ensure that I haven't plugged in the filament sensor incorrectly on the board.

Any ideas on how I can go about finding the cause of the issue, or links to info on the MK2.5 that I can't seem to find anywhere? The help page for the MK2.5 is still up, but the only info there is the printing handbook, which doesn't have the actual upgrade/build instructions, and the only RAMBO wiring diagram (pg 67) doesn't show the filament sensor or its orientation.

Here are a few pictures showing the back of the extruder to show that it's an MK2.5, the LED display showing the firmware version (latest as of last October), and then the display in Support->Sensor Info where you can see the real-time sensor data as you put filament in and out of the filament sensor area.

https://photos.app.goo.gl/CSPyFdJ4CxZp53rL9

You can see from the short video that the numbers do change when I put filament in and pull it out, but I have no idea if it indicates it's working properly or not. The B and S values change is small but consistent. The Xd is always zero, and the Yd changes by a value of several hundred, but it doesn't seem to return to its original value when I pull the filament back out. I have no idea if that's OK or not. To be honest, I don't even know if any of this is related to the filament sensor not working anymore.