One thing which has always been a concern of mine. When the part was carburized in manufacture the carbon was added to some depth to the surface. This was then hardened to form the "case". Even though the colors fade the carbon is still there & unless annealed it still has its hard case. When the part is re-carburized what effect does this have on the original. what if a different medium is used, is it absolutely going to be compatible with what was used the first time etc. Does this re-carburization add to the depth of the case, perhaps making it more brittle. All things to be considered I believe.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra