71 240 ammeter dips - VR?

I recently ( back in Sept) had the voltage regulator, battery and alternator replaced in my '71 240. Afterwards, the ammeter would fluctuate between midway and slightly-above-midway depending upon what I had "on" (lights, wipers, etc.). The needle generally stayed steady, though it would bounce slightly when I would rev the engine or flip things on and off. Nothing out of the ordinary.

A couple of days ago as I was driving home from work I noticed that the ammeter's needle was now staying steadily below midway as I ran the wipers and lights. I turned both off and the needled balanced out. My assumption is that I am draining the battery when this happens and that it is not recharging.

I checked all connections between the battery, VR, alternator, starter, etc. Everything looks fine and is connected. I even checked the fusebox. I have not taken a look INSIDE the VR and am planning on taking the car in to be looked at by my mechanic, but wanted to see if there was anything else that could possibly be causing this. Any ideas / suggestions? Thanks