Leak coming from A833 bell housing. Help!

I did not put this engine and 4 speed a833 in and I have not rebuilt a tranny before. I took my 69 dart out today and came back with a pretty good leak coming from the bell housing cover. I took it off and it looks to be coming from maybe the input bearing retainer in the transmission? Smelled the fluid and it's definitely trans fluid. Should I attempt to replace the retainer? Could it be something else? Would I get fleeced for this "little" thing by taking it to a transmission shop? Any help would be greatly appreciated.

IMG_0022.JPG