Sharing knowledge, I have been building cars for over 40 years. Since we always had a speedo cable going to the speedometer, leaks were not a issue. So I have a 46 chevy panel that started leaking tranny fluid at the classic industries speedo sending unit mounted to the side of the th350 tranny. In all my years I never noticed that the tranny bullet has a pair of O-rings inside of it to seal the speedo gear. So if you have a cable or sending unit leak, it is highly possible that the bullet seals are shoot.