I have this strange leak on the back of the tramssion. Is hard to pinpont. I have replaced the speed sensor and still the same. Looks like its coming from the top.

I only see two places where it could leak. the shifter piston or the rear main seal. I will attach a pic from a diagram.

Could it be actually be leaking form the shifter piston?
Should I just change the extension housing fluid.(thats what i found out is called - the rear seal. ?
I already have the transmission dropped. So im ready to do what it takes to stop that leak

I have some screen shot that hopefully you can help me with.

Its a 2006 mustang gt 55Kmiles. Manual transmission

http://www.flickr.com/x/t/0094009/photos/7553027@N02/9253811875/

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I would expect there would be a shift rail seal so it's possible it could be leaking. Check the rail shaft for scoring before blaming the seal. Fluid level should be 1/2" below the fill plug, if someone has added or changed fluid before. A plugged trans vent can also cause internal pressures to rise with heat and force fluid by a seal.