Transmission is leaking fluid but still works full

--Could be coming from the front seal, extension housing and fluid pan gasket you need to pinpoint it-The cost of repairs varies with location-shop around for the lowest cost with a reputable tranny shop-

Just to add to this one if its coming from between the engine and transmission its most likely the front seal aka the tcc seal. There really isnt a extension housing only a torque convertor housing. Which usually only leaks when the output bearing goes bad and the bearing race cuts thru the housing. Which if that happened you know it because it would turn your transmission fluid greyish silver. The transmission pan is under the battery its easy to see if thats leaking. But if your loosing a lot of fluid fast I would say its not that. To replace the seal lets say 100 for parts plus alignment 80. Labor would be about 800-1,000.