I think it's kind of impossible for an average ST 1100 owner to make an objective evaluation of how well the anti-dive system is working, or whether it is working at all. I think the only way such an evaluation could be made would be to test ride your motorcycle, then immediately test-ride another ST 1100 that is known to have a fully-functional and properly operating anti-dive system. Even then, it would be tough because you would only have one or two seconds (during the application of forceful front wheel braking) to observe the effects of the anti-dive system.
I rebuild my anti-dive system every 10 years. It's not expensive or difficult to do, I just replace all the components that are subject to deterioration, and at the same time, thoroughly flush out the front fork system and replace any front fork components that are worn. Although I think the whole front fork system works better after this work is completed, it's still very difficult to describe what "before and after" is like, because several days pass between the last ride before the rebuild, and the first ride after all the work is done.
Michael