Circlip thingy

That is a type of Speed-Nut. Hunt around Mcmaster-Carr, and other hardware suppliers to find it- have the diameters handy!

You may be able to remove it by using a two or three dental picks and carefully prying up a few of the teeth with the picks simultaneously. I've done it with just two hands but then I am ambidextrous. An extra pair of hands might help...

John :-#)#

Cut up a clear blister pack from any commercial product with a razor or X-Acto into very narrow slivers. Bend each of the 5 spokes up a bit with a dental pick and work a plastic sliver under each one. You should be able to walk the clip up from the shaft by rocking it.