Why do I not have reverse when I have other gears?

700R4 or 350 turbo transmission

At first I started losing reverse and O/D gears, so I started driving in 2, 1 gears then I lost them. I was then told it was due to lack of tranny fluid cuz I had a worn out rear seal gasket. So i replaced that and put my drive shaft back in and it looked as if it was not in all the way but I had all my gears back except for reverse. I even put Lucas stop slip fix and I still dont have reverse, am I doing something wrong or what, cuz I don't know?