[morzh]

What Arran said.

I did several.
Sometimes the circlips are flat E-type, and sometimes they are square x-section type. What you have seems to be the latter.

First I take something hard and long with a flat surface (a big screwdriver, a metal bar), and press against the gap in the clip. I do it while holding the pot or the switch with both my hands (pushing it with the thumbs) while pressing that bar agains the gap, pulling the bar with the rest of the fingers. The goal is to widen the gap and to see a little of the space between the clip and the groove it is in.
If you could stick an awl (large sharp metal pick) in that gap and start pulling - great. Look for the clip to not fly across the room. This is why it is called "Jesus clip."
Also look for the pick not to slip and end up in your hand/eye/beerbelly (if you got one).

Some folks use two bent picks to pull the ends apart. On a couple of occasions I successfully used a pair of neednose pliers to accomplish it.

Nest step: if it is really frozen, well, soak is not necessary, but introducing some penetrating oil (PB Blaster) and wait a bit.
Use heat on the bushing (not on the contact phenolic piece).

Apply force ( torque) against the bushing, NOT the board. Which could be accomplished by bolting the switch back in place and toruqing CCW.

Usually works fine.