Lately I've noticed that the needle on the tacho on my EL Fairmont isn't returning to the point where it should be once the car is turned off. The needle drops down most of the way but doesn't return to where it should be. When I start the car up the needle then returns to where it should be for a split second then proceeds to work normally.
What could be causing that? Could it be something simple like some dust hindering how it works?

Is it a constant occurrence or does it only happen in cold wet weather? I ask because the other old EF wag used to do the same in those conditions, when I stripped it for parts I discovered the connectors for the cluster had corrosion on them.. I'd check them 1st. If not strip the cluster down and blow any dust etc out, but I would have thought dust would prevent it from dropping as you say when you restart the car.

It does it in all types of weather.
When you say "Connectors for the cluster" do you mean then plugs that plug into the bottom of the cluster?

Yes.

I took the cluster out and cleaned the connectors and the plugs but it's still doing the same thing. Inside the dash is clean and dust free too. I'm at a loos as to why it could be happening.