Those itty-bitty ones are kinda hard to stake, and keep from deforming. The tenon is probably the narrow 0.055" one also.
If you upgrade, then either dovetail the slide or modify the slide for the wider .125" tenon. If you try to go with a larger sight and the narrow tenon you will regret it not to far down the road.
If you restake the sight, degrease it thoroughly first. Afterwards a tiny amount of green Loctite may help keep it stable.