I did consider pumps, but i would probably have to make them custom to fit in the size/ performance i need. a concern i had was the 1 second minimum to maximum actuation requirement - would a small pump be fast enough? likely driven by nema8 stepper.
i considered that first (Using air) and did real world testing with that concept (3 way solenoid + stepper motor needle valve). getting the varying actuation amounts and speed in a small package (still haven't achieved size, but i can with a custom machined manifold) was very hard, and I still don't even know how i was (or am) going to get the air source to fit, thus a non-compressible liquid was worth a shot to try next i figured, since it would be entirely closed loop - thus no air tank, compressor, etc. also lower power draw.
as for @DTJ 's proposal, i don't believe using your method would give me any extra room, and would actually take up more space. if i could have rods sticking out the back, it would be nice, but due to size constraints i cannot.
since the ideal solution, sealing the axis of the actuator seems impossible as told to me by two people here so far, I have designed this non ideal solution, that only gives me two inches of fluid actuation at about 0.65" ID diameter. I believe this should be enough though. here are some images.
i am still very open to suggestions. thanks.