brazed tubes can leak as well. I had that happen in my last house. Little leaks are hard to find, the first time I had the system refilled the tech couldn't find anything and put some sealer in. The next time the tech did the same and was disconnecting the fill lines when he saw a dark spot, then he emptied the lines and did the proper fix.
Sure, anything can leak. Brazed fittings when executed properly and tested are much less likely to _start leaking_. the issue is that the flares have a tendency to work harden during the constant vibration and thermal cycling and eventually give up.
