doesn't this unit have a master cylinder on both sides? the one on the right side is for the brakes only, while the one on the left side is brakes and inching valve (transmission decoupler) and what you may be calling a "line lock" might either be a crossover, or someone installed a mico-lock kit (which may be part of your ?problem?). the brake fluid from the left side master cylinder will be the one that pushes on a valve on the side of the transmission (under the drivers foot area).