Plastic can age and become brittle, and also "creep" over time. I'd go with one with a brass or copper sheet bushing like originally, BUT, add a touch of lube at that sliding interface. I use a dab of anti-seize, but grease will work fine too. This will make the lever much easier to close, will not cause it to pop open, and improve durability.

If the aluminum QR cam is not too worn, you can also cut a new copper sheet to size after drilling a hole. No copper sheet? Find a penny old enough to be all copper and not copper clad over zinc. Hammer thinner on an anvil or some vises have an anvil area on top back. Might need to anneal the penny with a torch to make the copper more ductile. If you have an empty rifle or pistol cartridge case that is typical brass, that might also provide raw material. I've used a copper-jacketed rifle bullet, melted the lead out, and used the jacket to make a "socket" for a rim with crack at the spoke hole, to transfer spoke load to inner rim wall, just like double socketed rims. That copper jacket would also work for your application.