My 727 automatic trans is leaking at the speedometer cable. Took the housing with markings 21/25 to local trans shop old-timer that use to work on these replaced the seal, acually put 2 seals in the housing. drive it 25 miles and it still leaks. trans shop guy thinks the housing should have a gear in there with 21/25 teeth. even though year one lists only 1 housing. Year one shows gears starting at 24 teeth thru 43 teeth.
My gear is a RED 36 teeth and is acurate
ANY ONE OUT IN MOPAR LAND HAVE ANY INPUT on why this thing leaks????

The year One housing is the version that accepts three different diameter pinions the smallest being 26 teeth, if the housing is marked 21-25 it is for the pinions with that tooth count and only those should be used in it.

I'm surprised you were even able to install it with the 36 tooth gear but the excessive side load from the oversized gear is probably the reason for the continued leak.

Could be a warn part not letting the seal do its job, or the seals weren't any good. Is the leak at the adapter itself? Is the cable leaking?(indicating the pinion seal is leaking) Is the leak coming from the extension housing? (mating gasket, or even the retainer srew for the speedo drive)

Just a few questions that may help find the answer.

I think this is the housing you need.
http://www.moparts.org/Tech/Archive/auto/21.html