I have a 2000 SS Camaro that I put a silver gauge overlay on. It went on ok but the oil pressure gauge doesn't work right.
When you start the car up it is ok, it works like it should, but when you turn the car off the gauge does not retract to zero.
Now if you let the car sit, and then turn the key to run it will reset to zero and then you start the car and it works.

 

Did you make sure that you put the needle back on in the correct position? Also, is there a slight bulge/small bubble under the overlay around the oil pressure gauge?

When I put my overlay in I took a picture of the gauge cluster with needle position and then took them off and peeled off the factory black overlay off the plastic, then put the white over it. I did this because it made the needles touch the gauge face with both the factory overlay and the aftermarket.

 

I did take a picture of gauge set, and marked them too.The gauge just dont zero out unless you reset with the key.

 

mine doesnt zero either. what i thought was that theres servo moving the needle, and when you stop the engine, and the oil pressure drops, the gauge cluster is no longer getting any power, making the needle stop where it is. if thats not normal, maybe i should be worried too.

 

I think it's normal, mine has always stayed around 40 on shut down. Only gauge that doesn't zero out.