Hey guys I have a 76 F150 with a C6 that's pouring transmission fluid on the ground anytime I put her in drive. Strange thing is it doesn't happen in reverse or park, just in drive. The fluid is pouring off the crossmember, but I haven't been able to work on it long enough to trace the source (the truck is in a restricted access parking lot).

I've checked the tranny coolant lines (I replaced them less than a year ago, tight no signs of leaks), the pan gasket (no signs of leaks), the vacuum modulator (no fluid in it or the vacuum line), and the speedo cable input (a little damp around the opening, but did not see fluid coming out when the leak was occurring). All seem fine.

So I'm thinking extension housing seal? Am I correct that the seal is located almost right above the crossmember? If that ruptured, would that leak only while in forward gear? Looking for any input on this, so I have a plan of action when I can get back to the truck. Thanks for any help you can provide.

Edit: I mean the extension housing gasket.