The Resistance to Attack by Aviation Phosphate Ester Fluids (of which Skydrol is) with Polycarbonate (Lexan) is listed as "Poor" and Skydrol "Not Recommended."
See also the associated links.
skydrol
Nitrile rubber is not compatible with Skydrol, a type of hydraulic fluid used in aviation, because Skydrol contains phosphate esters that can cause nitrile rubber to swell, soften, or degrade. This chemical reaction compromises the integrity and performance of the rubber, leading to potential failure in applications where reliable sealing and durability are critical. For applications involving Skydrol, alternative materials such as fluorocarbon or other specially formulated elastomers are recommended.
With check valves,selector valves,actuators,restricter valves and sequence valve,the most common hydraulic fluid is called skydrol,the fluid starts and the reservoir (tank) then it pass throw the EDP or the GDP (engine driven pump note:for flight use only) (generator driven pump note:for ground use only)and creates a flow which os converted into pressure,PSI (pressure per square inch)it reaches 3000 PSI and that force makes the landing gear go up and down