........(bearing) in your Oberon (or OE) clutch slave - just found mine worn flat to circa third of diameter - not seen that before - replacing it didn't cure my dragging and slipping Sigma though.

How can this be? Were your clutch springs tightened so much that they were always applying pressure on the ball?
Perhaps one plate missing? New rod that is too long?
Dunno just doesn't make sense...

Push rod can't spin 'cos of the locating pin - end of rod only slightly dished and Sigma clutch hasn't been touched in 60k+ miles - might be just a soft ball but clutch due an overhaul and will replace rod as well.

Ball bearing has been binned and the rod reinstalled - not much to see of either really, though.

No issues re lever adjustment and, whilst a new ball bearing hasn't solved the clutch drag, it may be that fitting the new rod as well may.

I have always understood that the clutch slave, ball bearing and rod were always under applied pressure from the clutch pressure plate and not 'slack' when the clutch is fully engaged? If I'm wrong, that's another reason why I need to overhaul the clutch.

Pin still there and clutch slippage rapidly worsening - new tyres, major service, new head bearings, new fork seals and full/part new clutch = expensive couple of weeks.

Plates more badly worn than I thought as clutch has now completely given up - should not have compared the plates wear to my 996S which seem to be permanently knackered - so slave ball and push rod wear must be down to pressure plate load, bearing on push rod rather than clutch pack.

Makes sense now with the benefit of hindsight...