What's going wrong here?

[Skunksmash]

For some reason I can't seem to fix this leak. My 700-R4 in my 87 Silverado 2WD 5.7L is leaking out of the speedometer cable port. I ordered a new seal for the inside, and put it in to the best of my ability. I couldn't tell any difference between the way the old seal was in, and the way that I put the new one in. Yet it still leaks. Its the last rubber seal right before you get to the speedometer cable itself.

I don't understand why its still leaking. Its extremely irritating to have done the proper fix for something and still have it be screwing up. Does anyone know if fluid getting in the speedometer cable, can somehow harm the cable? Or perhaps, the speedometer itself?