Ok that is the 30RH and it probably has the same issue as the 32RH does when a 231 previously set up for the AX-15 is bolted to it.
What you probably need is an extended rear output shaft seal for your 30RH but I don't know if it uses the same seal as the 32RH does. Several sources of the extended 32RH output shaft seal include Teraflex, Summit Racing, and either Advance Adapters or JB Conversions... one of those last two also carries it but I forget which.
I would call them and see if they can tell you if the 32RH extended output shaft seal they sell is also usable on your 30RH.
If nothing else, you can replace your 231's input shaft to the longer version needed to properly seal inside the 30RH.
This assumes the problem is that they installed a 231 that had previously been bolted up to an AX-5 5-speed so its input shaft is not long enough to seal the 30RH's output shaft.