ORIGINAL: eaticus

Let me have a go at it...

The master cylinder and slave cylinder must match in size (bore and shaft dia); just purchase two identical cylinders. see attached illustration.

Installed the system in the model ''dry'' to size the length of the lines. remove the lines from one of the cylinders (but leave the other attached).
Soak the cylinders and lines in a tub of hydraulic fluid (a light weight oil such as 3-in-1 would work as hydraulic fluid). Assemble the lines back on the cylinder ports. avoid trapping air in the lines. (If necessary, attach the lines in thetub of fluid).

That should do it...

PS: Avoid large bore cylinders as it will need to push a lot of fluid, thus need a larger servo. Smaller bore cylinders will have a better steering response.

The steering cylinder that you have shown should work just fine!