Replaced, as it turned out rather pointlessly, the bearing in the AC idler pulley. Swapped a grumbly one a while back which ran quiet but had some play in it. Machined out the old one tonight and pushed in new one. Silky smooth and still has exactly the same play in the bearing. Not the spigot, but the actual inner and outer race. I guess as long as it's not side loaded it doesn't matter. Oh well. Wasn't difficult nor expensive. They are staked in and truck to remove without a lathe. The staked bit is actually a steel disc cover and NOT the race itself.