Speedo and trans issue

Hey guys, hoping someone can help, last week I pulled the speedo cable out from the trans housing on my son's 64 Dart with a 904 trans to look at the gear as I was replacing the speedo cable. I had a heck of a time putting it back in but it finally went after tapping on it for awhile. I used an aftermarket universal cable with the square end that crimps on the end after you cut it to length. Anyway, it didn't work, it moved the needle to about twenty miles an hour as I was testing it and then made some funny noise's and quit working. I unscrewed the cable from the back of the speedo and the crimped square piece had come off. The cable is stuck in the housing now and won't pull out so I went to pull the entire cable housing from the trans hoping to maybe find a factory replacement but as I started pulling it out the trans started draining, it didn't do that last week when I pulled it out so here's my long-winded question, why is it draining and should there be fluid in the tail cone of the trans? and can anyone tell me where I can find a factory replacement cable. Thanks in advance,
Eric D.