I think ammeters can suffer badly from vibration, especially the ones with the needle above the face. The later type with needle below the face, like the first photo, are a bit more robust. These came in, with 8 -8 face with the A65 in 1962 and, according to Lucas, fitted on the Super Rocket and RGS for 1963 season.
If you turn this later one over and probably remove some sealant (photo 2), you find the little screw in photo 3, which may, if screwed in carefully provide some damping for the needle and stop it going all over the place. Screw it in too far and it locks up, but worth a try might extend its like and nothing to loose if you think it is unservicable?
With the earlier type there is also a little screw, photo 3.
These photos are from real old Lucas ammeters, I dont know if the new lucas have the screws.