could be the other line or could be a gally plug. the only way to tell is clean it up with brake clean, tear it down and fire it up. then watch and see.
what about a rear main seal? is it common for those to start leaking? i have cleaned up and cant tell for the life of me. i just installed the chip again so if theres a leak, i guess the chip will make it more noticeable if i can ever find it.