'92 S-10 Blazer trans. Case keeps overfilling

1992 S10 Blazer, auto, push button 4x4, 210,000 km. This truck runs well except for the following, my transfer case is completely filling with trans. Oil. I know that the trans. Has been rebuilt twice. I'm sure that the rear shaft seal is not under pressure so it doesn't make sense that is keeps filling the T-case way past the fill plug, even the three vacuum lines at the top have trans. Oil in it. I have no idea what to think of this because the level is much higher than in the trans. If you fellas have any idea what may be happening please drop me a hint.