Can anyone please tell me how to remove, what I believe is, the retaining ring...see pic.
you need to force the plug down a bit, and keep it there, so you can get an awl or very small screwdriver under the ring (near an end). Once out of its groove the retaining ring will promptly fly out of the fork leg and hide in the most unaccessable part of your workshop.
This were having a loving spouse or a child you can order around comes in handy, You use something to press down on the plug, then you or the person you got helping you can use a pick and needle nose pliers to pull the retain ring out, or you can do it alone and wear safety glasses because when you do nudge the ring out it will either hit you in the eye or go flying across the room, you will see it hit the first time and then it is gone. After you get everything set down and the safety glasses off you will then need your CSI flashlight and knee pads to search the floor to find said retaining ring, after exhausting your large vocabulary of curse and swear words, you might find it were yo wonder how it managed to get there.
So let's say I get the retaining ring out. is it really hard to get back in? Do I need special tools?
nope I just used needle nose pliers and a old dental pick to get it in place. So a screwdriver will work.
Thanks for your help!