Thanks John - I've had a few goes with some scrappy lenses and am starting to get the feel of it. Not having the right tools is my biggest handicap at the moment so I think a look Microtools is the first step.
It'd be very useful if I could find some web articles showing exploded diagrams and step instructions for dealing with specific lenses.
Some of the lenses I sell on, so it's not worth paying a repairer to do the work as this costs more than the lens is worth.