A common problem on the GL1800 is air gets in the line for the hydraulic preload adjuster. So we recommend bleeding the preload adjuster and topping it off with fresh oil plus installing our new Steel Braided Line. The steel braided line replaces the poor quality OEM plastic line.
The OEM line tends to well over time which allows air in the system. When there is air in the system you do not have a full range of adjustment with the preload adjuster. It is not uncommon for us to see the adjuster not moving until 7-10 due to air in the system.
With our steel braided line, manufactured specifically for the GL1800 the system will be sealed much better than OEM very similar to steel braided lines in a brake system.