If you are only trying to stop a leak I would not fool with valve body
either. I have done a few of the 2nd servo pistons with the trans in the
vehicle as well, If you don't have tool # OU812! to depress the piston you
will have to come up with a large lever (maybe a 2x4) and pry against the
trailing arm mount with a large socket on the piston cover to depress the
spring (do this to remove clip as well or you might bend or break it .) You
might practice this once with the old seal before doing it with the new one
that way you know exactly what your doing when you go together with the new
seal.
Do plan on replacing all of those seals on the piston and check the piston
where the rod pushes on it for cracks in the aluminum.
Good luck!
Jeff
ATL.
87' westy