Any question answered...

Using light spray lube (say GT85) give a thorough spray inside the shifters mechanism from all angles possible, this should magically restore crisp shifting, next though you need to get some heavy spray grease, as used for motorbike chains or chainsaws, and spray this inside as well (for longterm lubrication)

Found that advice on a thread here somewhere (can't remember where) after a shop told me the shifter was knackered and needed replacing, tried that and it worked a treat. Can't hurt to try?

Motorbike chain lube is very very sticky to deal with high speed chains. I would never use this in my shifters!

Once made the mistake of using some of my Dad's moto chain lube on my bmx chain.. fail.