Hi ranger lower control piston seals

[Spo307]

I am in the process of replacing the Teflon and rubber ring seal that go around the piston in the cups on the lower controls these are where the tubes from the joystick in the upper controls come into the lower controls. Has anybody changed these I was told to use a three-quarter copper feral to compress the new Teflon ring so it will fit in the cup? Thank you