I don't know how much mechanical and electronic experience you have, but I have owned a '91 4matic wagon for 5 years and do 95% or so of my own work on the car. The 4matic transfer case is one of the components that I would be the MOST reluctant to replace in my own garage. Most independent and factory dealers don't even have anyone with deep 4matic experience.
The transfer case is a known weakness in the 4matic system, the original cases typically don't last past about 75 - 100 k miles. I know many 4matic owners and the common practice is to replace the failed case with a new factory unit. I have heard the new units have improved design. I can only give you my experience. My car had the xfer case replaced with a factory new unit at 75 k miles, and it's working fine at 216 k miles now . (SERIOUS WOOD KNOCKING SOUND) I'm rather obsessive on maintenance.
The bottom line is that, depending upon where you obtained the replacement, you may have worsened the problem. The system is awesome when it works, but the system is very complex and not for the faint of heart when it comes to long term maintenance and ownership.