If it came with a copper washer, and the surface around the threaded fitting on the WC is machined flat to accept this copper washer, than more than likely that is what you need, with the banjo fitting.
And what you think is the bubble flare inside is just the bottom of a drilled hole for the banjo bolt.
A brake line or fitting should easily screw in place before it bottoms out, it should not be hard to assemble.
Grigg
