Speedo cable leak?

[Skunksmash]

I'm still having trouble with my 700R4 leaking. In my 87 silverado 2WD 5.7L. It has that speedometer compensator thing that the speedometer cable plugs into. Its there to sort of adjust for larger tire sizes than stock. Then that thing, the compensator unit, goes right into the side of the trans.

Well something is leaking trans fluid. And I think that it may actually be the cable itself. I went to take the whole assembly apart and look for the bad seal, but when I unscrewed the speedometer cable, a thin black plastic thing fell out. It looks like it sort of went up inside the speedo cable end somewhere.

Can a bad speedo cable seal cause a leak in some vehicles? Cause I'm starting to think that's what's causing mine. I couldn't even get the little black plastic thing to go back on so I just left it off and screwed the speedo cable back in. Now my speedometer gauge doesn't work. Could it be possible that all I need is just a new speedometer cable? I'm used to my old truck's turbo 350 where the speedo cable seal against any fluid and when you took it off, it was dry other than maybe a little grease.