Make sure the lines aren't rubbing something, and that the fittings are good as well. Weak point is where the fittings join the line and any fittings with bends, as the seal can weaken. Do you have the nylon-braided lines or steel-braided? I changed mine out to steel and made sure that the lines were tie-wrapped to keep them from moving and rubbing against an intercooler clamp or any of those screws for the plastic underpan. I have an ER Sport kit to replace my factory unit, so I'm not sure if yours is mounted similarly.
2013 F30 335i M-Sport 8AT/MPE/MPPK, 2011 128i M-sport Cabrio 6MT/PE