What is the recommended lubricant please?

A bit of copper grease would be enough.

Edited 23 December, 20178 yr by LGM

I just use a "touch" of silicon grease which is said not to annoy/swell the rubber "dampers", prior to that I'd just clean them up every year and fit them back in "dry".

Red rubber grease. Avoid using cooper slip as already said it can swell rubber and cause sticking and seizing problems. 

I use ceramic brake grease.