Case Hardeining

["Bob Nogueira" <nogera@worldnet.att.net>]

Can a gear be case hardened a second time? I'm rebuilding a transmission (
for which replacement parts are no longer available) and one of the gears
appears to have a couple of teeth  that  have been exposed to moisture. No
heavy rust but it appears to have removed the case hardening.  Am I correct
in the believe that the hardening is only on the surface and does not go
very deep?  .
Bob