The job is completed and the new windscreen adjuster is in place and working fine. Total time for me to complete the job of removing the fairings, fitting and testing the adjuster and refitting the fairings was about 4.5 hours. Most of this was spent on the fairings. Total cost to me by ordering the part from the USA and fitting it myself was $480AUD. The part alone from an Aussie Honda dealer was around $1,400.
The screen is moved by two cables which are pushed and pulled by a single worm gear. This gear had worn, and allowed one of the cables to slip and thus the two sides of the screen adjuster mechanism got out of sync.
The first photo shows the old adjuster mechanism in place and ready for removal. It's the large "H" shaped assembly.
The second photo shows the old mechanism, separated from the bike. The cables feed into the aluminium cast gearbox in the centre, and buried deep in this gearbox is the drive gear. The cables push and pull the sliders in the tracks on each side. This whole part is sold as a single assembly and is what cost me $480
The third photo shows the back of the adjuster assembly.
The fourth photo shows the wear to the gear which caused the failure towards the bottom of the gear. Towards the top there is some wear showing where the other cable interfaces with the gear.
I'm unsure of what has caused to the wear, but having a larger than standard screen may have been a contributor, as it would put more load on the mechanism when height adjustments are made at highway speeds.
More info on this mechanism can be found at
http://www.st-riders.net/index.php?topic=7125.0 which was pointed out to me by tj189.