Not disagreeing with Keith’s posting – most valuable to have a guide to dismantling the swivel – but just to let you all know: although I did buy a pack of balls, when I got the furler apart, there was nothing wrong with the balls, not even a sign of wear/pitting. BUT, there was a build-up of repeated squirts of silicone lube; this had left a gunge which was certainly affecting the top swivel.
In the end, a thorough clean-up (and no further squirts of silicone lube) seems to have left the swivel in good condition. That was 2 years ago
Martin (3912)
The Flying Fifteen Blog 
As I said a dry lubricated item, squirts of silicone affecting the performance of the unit. It appears dismantling and cleaning fixed the problem, but in my experience the balls do wear and the units do need serviced from time to time. I wouldn’t have ever imagined that this would need to be done with any degree of frequency, however if the unit (top or bottom) is becoming stiff or not functioning as it should a quick service usually fixes the problem. We posted as not many realise how easy it actually is.
Hi,
I agree with Martin never squirt or lubricate with any stuff on those dull beige balls. It’s very un-scientific but new balls bounce from up from a hard surface ceramic/concrete almost to the height they fell from. So if they do not, however good they might look, they are not up to snuff.
Given the above I found it very useful to dismantle my furler over a large plastic bowl.