Speed Sensor Leaks Oil
 

Anyone have an idea on how to prevent a Speed Sensor from leaking oil onto my exhaust pipe? I've taken it out throughly cleaned the sensor and installed a new O-ring and put some sealer around it to help prevent leaking.But it still leakes oil.Other than buying a new one?(If that will even help)Is there something else I can try? Is there any possible reasons why oil might be leaking from a part that looks in good shape? Is it possible oil is getting into the transmission and building up pressure?
88Mustang 5.0 GT 5 speed