It sounds like it is a torque converter seal thats leaking. I strongly encourage having the transmission looked at when you remove it to make sure that you dont have any issues that is causing the seal to go out. Yes they do go out with old age, but worth looking into. I also recommend a replacement torque converter and all new fluids while you have it out. Might as well do the rear extension housing seal on the rear tailshaft of the transmission. The bellhousing you are talking about replacing is not needed unless you broke yours somehow.