1968 C4 transmission question.....

[myname182]

I have a 1968 mustang with a C4 transmission. About a month and a half ago i took my car to local mechanic because it was leaking oil from the transmisison...He went ahead and changed the pan gasket and that was it....the tranny continued to leak, so i went back and he said he had just put too much oil in it and it was leaking from the top spout. So he removed some oil and it still kept leaking. It was no longer leaking from the pan, only from somewhere in the top...I asked him what type of oil he put in it and he said Dextron, i usually put type F...does that make a difference, is that why it may leaking?...i thought you could only put type F...he said dextron is ok...or why could it be leaking??? Help