97 Jetta Transmission Seal problems

recently my jetta started leaking transmission fluid from where the drivers
side drive flange goes into the transmission. I took the halfshaft out and
when inspecting it noticed that it was missing a seal where the flange
meets the transmission. I noticed this because there was a seal on the
passenger side and not on the drivers side. But inside where the halfshaft
goes into the transmission i noticed a rubber gasket or something. I tried
taking this out thinking that it was the faulty part needing to be
replaced but could not remove it. I ended up buying a seal and putting the
halfshaft back on the car. Upon inspection of the car both sides now look
the same where the halfshafts go into the transmission. But upon driving
the car the drivers side is still leaking. I am confused as to what to do
because im not sure what I did wrong. I'm not sure if I installed
something incorrectly or what. I like working on cars but I'm not all that
knowledgeable about everything so any input would be greatly appreciated.
Thanks in advance.