i doubt anyone cares, but i'll post an update for closure purposes and for future searches...
i ended up using the old reverse servo assembly out of my stock tranny (with lighter duty springs) and stole the newer designed piston o-ring from the rebuilt tranny. used the cap with stock o-ring from old tranny. set it in place, tap-tap-tap with blunt object to seat it in the cylinder (low enough to install snap ring).
no leaks.
could just be the reverse servo assembly out of the zzp rebuilt tranny wasn't seating just perfect and maybe I could have just put that same one back in after cleaning it up. but either way, the car doesn't leak from that area.
the rebuilt tranny had been sitting in a driveway paperweight for over a year before I installed it. so maybe the o-ring on the reverse servo cap had shrunken a little bit too. whereas the cap on the reverse servo that i took out of my stock tranny had just been in a functioning vehicle.
that's it.
james
