Hello Paul, I'm doing the same thing at the moment. Stick your phone torch into the hole and have a look. I'm no expert but I think it's model dependent. If there is a bush there, mine had disappeared completely. Rubbery dirt/dust in that area might be a clue.
I have been told that the bush for mine is 90622363-POLY at Wins. Again, I'm no expert, so don't quote me, but I'm ordering both bushes this week, and even if your Nylon seat bush looks Ok, which mine does also, apparently it still might be failing.