The monkey-motion is shown in carpartsmanual.  Looks like it has a bigger o-ring.  

http://www.carpartsmanual.com/datsun/Z-1969-1978/power-train/transmission-control/4-speed/to-aug-71

Edited May 17, 20204 yr by Zed Head

I think the monkey motion used two o-rings, but it is a really long time ago since I seen an A apart.

All the o-rings and lip seals are still easy to find at any hydraulics shop. Just remember to ask for NBR or Fluorelastomer (Viton). Don't use EPDMwith mineral oil, that is used in the brake and clutch systems.

I’ve got the parts covered because I have the best parts guy - Riley@lynchburgnissan .

He knew the O-rings that it needed and I have them coming . I’m not sure I want to fight this battle or take it to the shop . After reading this thread I’m a little intimidated . Plus I have my hands full fixing many other things on this car . 
Come to think of it - I think I have a spare 4 speed myself . But swapping out tailshafts could be a gamble not knowing condition of it . 
Thanks guys - I need the help