[graham.hobart (Graham stevens)]

Hello, on my FS 60 there is a knurled knob which allows for rotation of the diagonal and also a knurled knob with a plastic washer inside it which grips the eye piece barrel. For some reason the bit that allows for rotation of the diagonal has jammed into the smaller black knurled piece- so I can only swing my eye piece one way currently.
Now I don't want to ruin it with pliers or mole grips- so does anyone have any idea how I can loosen this without too much pressure which will deform the ring?

see pic with arrow..
Graz