I noticed that my transmission is leaking a month or so ago but i didn't realize how bad it was. Tonight i noticed a big difference in driving it, it is very hard to shift, stiff, notchy, and scratchy. It is leaking for the rear of the transmission there is a black rubber circular piece sticking out wear it connects to the drive shaft. What part is this how could i fix this? Is it just a gasket of something more serious. Tommorow i am going to add a quart to it. btw it is a 5spd any help is greatly appreciated