I’ve been chasing leaks all winter on engine. Fixed all except one coolant leak. It’s a 347 with dart block. Was rebuilt and dart used about 10 years ago. Leak is dripping on rear pan on rear center flange. It’s coming from behind plate between tranny c4 and block. On engine side best I can tell. Did pressure test I checked top side of engine around intake and heads nothing. I don’t recall but I read there is a freeze plug on back of block. Does that sound likely. I’m getting close to pulling engine next. I have a feeling been doing awhile. Don’t drive car much. Any advice appreciated