You're positive it's the RMS that's leaking? I know that on the 4.0's the valve cover gasket can leak near the back and run down the back side of the block, making it look like the RMS is leaking. When was the last time the VC gasket was changed and what type of gasket is it (rubber or cork)?
The zj has been in my family's possession since 05 and I know it hasn't been changed since then. The gasket is rubber after I did the rms the leak had gotten slightly worse.