Tranny fluid in Transfer case

[GI Blazer]

I've noticed for quite a while that my speedo output on the xfer case wet with tranny fluid, (never thought much about it as there was never more than a couple of drops under the truck) I was changing out the rear output yolk on the case a couple days ago and tranny fluid came out when I pulled the yoke out. I then drained the case and it was full of tranny fluid. I had this once before and the tranny was rebuilt since then and while the tranny was down a seal on the front of the xcase was changed as well. Is this common? Anybody have drawings or diagrams that show the seals in the tranny and the xcase. I would like to fix this permanently.