Good clear photo showing the crack in the QR housing.
The vintage Shimano ones were machined steel, this one in the photo looks like it was die casted.
All you can really do is replace it with a better one.
If you want to be precise on the force, get a nut and bolt skewer. Those gets tightened with 7nm.
I use these on my personal bikes. I never remove the wheels anyways as I transport with a platform carrier.
Besides, they are just very long M5 bolts that use the same 4mm hex tool.