Man, I'm having the same issue with the locking switch on my new lux. I can't lock it. It was OK for a few days and now I can't budge it. I've tried the freezer and hot water thing. Can't get the locking ring loose. Anyone have any other suggestions?
Def Ian, spray it down with WD40 and let it sit or as Jas mentioned oil it - make sure you get a few drops into the backside around the nut. I prefer hot soapy water and let it soak as the oil is a pita to clean up. For giggles take the nut off the back(reverse threaded) and remove the spring and button and add a bit of oil around the axis hole into the threading.
Let it sit.
When replacing nut on the axis, you will notice the nut has different looking openings, place the nut so the side that looks "cupped" down and the flat side up. The button axis should protrude the nut by 1 mm. The threaded end of the axis is all that needs to contact battery, so check your nuts
The other way and the nut sits on top of the axis or flat on the axis and it causes the button to stick occasionally or the button to sit past the bottom of the ring and cause a button firing when sitting.