TH400 Leak question

[dmack91]

OK, so my TH400 has started leaking. I have searched the threads and am a bit confused.

It is leaking out of the speedo housing (outside 90 degree box/mount on the side of the trans). I have seen a pic of the large o-ring that goes on the round section that the speedo box goes into on the case (ring is around 1 3/4" round).

This doesn't appear to be where the leak is coming from. I am assuming there is an internal o-ring, but can't find a schematic that shows one for the 400. I have seen the pics of the "bullet" and o-ring for the TH350. Does the 400 have the same thing behind the speedo box or something different?

Just wanted to make sure what I am dealing with before I pull the speedo box part out of the side of the trans.

Thanks for the help.