You might just need new copper washers. You should have banjo fittings with hollow bolts if this is an original setup.

When used, they crush and the metal, work hardens from the pressure. They will not compress and fill voids the same again for the same torque value.

You may have trouble finding new ones the right size. In a last ditch effort you can try to anneal the old ones.

I use a propane torch, heat them to a dull cherry red and drop them in water.

If you are wondering if that sounds like hardening it is not. This is the method for non-ferrous metals.

Good luck
Phil