The Collaborative International Dictionary of English v.0.48:

Leakage \Leak"age\, n. [Cf. D. lekkage, for sense 1.]
   1. A leaking; also, the quantity that enters or issues by
      leaking.
      [1913 Webster]

   2. (Com.) An allowance of a certain rate per cent for the
      leaking of casks, or waste of liquors by leaking.
      [1913 Webster]

   3. (Elec.) A leak[3]; also; the quantity of electricity
      thus wasted.
      [Webster 1913 Suppl.]

Moby Thesaurus II by Grady Ward, 1.0:

78 Moby Thesaurus words for "leakage":
   ablation, access, admission, break, breakout, consumption,
   decrease, decrement, deliverance, delivery, depletion,
   depreciation, dissipation, distillation, drain, dribble, drip,
   dripping, drippings, drop, emergence, entrance, entree, entry,
   erosion, escape, escapism, evaporation, evasion, exhaustion,
   expenditure, extrication, flight, freeing, getaway, import,
   importation, importing, impoverishment, income, incoming,
   infiltration, ingoing, ingress, ingression, input, insertion,
   insinuation, intake, interpenetration, introduction, introgression,
   intrusion, issuance, issue, jailbreak, leak, leaking, liberation,
   outlet, penetration, percolation, prisonbreak, reception, release,
   rescue, riddance, seepage, setting-free, shrinkage, trickle, using,
   using up, vent, wastage, waste, wearing, wearing away