The Hauler's second ability never earned its slot in a fight — it widened a number you only ever met offline. It's gone. Ballast Oil takes the W key: the drone releases an oil bead that falls, blooms into a dark slick with a sheen of teal at its rim, and stuns whatever the slick reaches.
It works everywhere a Hauler needs it: in open water it stops a fleeing catch or a chase dead for a few seconds, and in the Abyssal Arena it holds the boss and pauses its attack clock — the same hold Electric Lasso grants, arrived at by a different craft.
It levels like every other class ability: each rank grows the slick's reach and how long the stun holds, and the bloom itself reads bigger and richer as it grows. Anyone who had trained Cargo Surge keeps every drill and level — the progress carries over to Ballast Oil whole.