Agree with Igofar and Suprasabre and another trick I have used (see the article) is to stick the fluid banjo fitting & copper crush washer “sandwich” together with some petroleum jelly (the stuff we used to use on baby’s bums when changing diapers).
It is sticky as heck so it is easy to line everything up before you try threading in that bolt - and if any gets into the brake fluid, it won’t cause any harm and will likely come out when you bleed the system.
The other key thing is: check the threads on the end of the bolt VERY carefully to make sure they are not misformed and that there is no burr that could prevent a smooth engagement of the bolt into the tapped hole.
One thing is for sure - after all the work of doing this job you do not want to strip or cross-thread that banjo bolt.
Pete