Ford - Explorer :: Turn Signal On Driver Side Not Working

My turn signal on the driver’s side isn’t working. It clicks quickly like when the bulb is out. The rear one on that side still works, but blinks quickly…which is normal when the front one isn’t working. It didn’t just stop working all at once. Over the course of the last year or more, it has gradually gone out--it would work for a few days and not for a while. A few months ago, it worked about half the time. Now it won’t ever work and I’m due for an inspection. Here is what I’ve determined so far:

It isn’t the bulb…I’ve tried a new bulb.

It isn’t the socket. I took the socket in my hand in the picture and switched it with the passenger side and the driver side still didn’t work and the passenger still did worked.

The plug that the socket goes into on the picture…I cleaned it good and used a little lubricant on it, but that didn’t work either. If that plug is bad, the local parts stores don’t carry it and can’t get it, so I'll have to go to the Ford House.