Without the sensor I can open the garage door with the remote control,
no problem. I can also close the door by pressing and holding the
hardwired pushbutton inside the garage. The only thing I can't do
right now is close the door with the remote because, by design, the
opener won't close the door if it can't find the sensor.

I'm sure it isn't an alignment problem since I've tried moving the
emitter directly in front of the receiver and the problem persists. I
tested the wiring too, since I've heard that is also a common problem
with beam sensors. It was all good.

I've been quoted $50 for a new sensor assembly. It would be a shame to
replace the whole thing when replacing a $2 component might do the
trick.