2000 Blazer with 185,000 miles but no engine related problems. But yesterday I developed an antifreeze leak, it appears to be out of the back of the engine all over the transmission. Doesn't appear to be coming from the head gaskets, any suggestions?

 

maybe the lower intake gasket. Blazers are bad for that. or a freeze plug

 

Yeah im guessing you've been slowly adding coolant for a long time now. And now the lower intake manifold gasket is bad and the leak is too big. It is very common on the 4.3 engine for that gasket to go bad. Its probably on its second gasket now and will need its 3rd.