If a cooling unit is determined to be bad, it needs to be rebuilt or replaced with a new one. Rebuilding is less expensive than new, and on the many extinct brands the only option available.
Rebuilding a cooling unit is the process of flushing, inspecting, repairing, re-foaming, and recharging the cooling unit. Although there is always a specific cause to a cooling unit failure that needs to be repaired, a reputable rebuilder will also inspect and replace other deteriorated and partially clogged pipes in the cooling unit in an effort to increase its life span and to be able to give a warranty.
Since even a "simple" repair requires that the cooling unit be removed from the refrigerator, flushed, and recharged, it's only practical and cost effective to go the extra step for longevity.