Thanks Spakka.
I had come to the conclusion that I'd wait and see if it gets any worse.
One plus point is that it's not so serious that it affects circulation. I used to race in cycling at quite a high level and still train regularly. But I can easily maintain a fast pace for several miles without breathing through my mouth, so I'm aware that my circulation's in pretty good shape.
It's not painful to touch at the time, but prodding it leaves a dull unpleasant feeling for several hours afterwards.
Anyway, whilst not impressed by the possibility of carrying "incompetent" bodily components, I am happy to receive any advice that says forget about it, it's normal.