From a biased background i just can't see it working. We used to use hydraulic manipulators with microscopes - much smaller scale than a telescope but needed sub-micron accuracy. There were water ones and they were terrible - if any air got into the system or formed from water that wasn't properly degassed then you'd get this uncontrollable drift. Then there were oil ones - but again you could still get air bubbles and leaks. Funnily enough, stepper and servo motors took over in the 80s.
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