Well, there we go.

Having worked with silicone-based fluids when I was in a research lab, I can say that they do break down. Noticeable? No. Measurable? Yes. The point I was trying to make is that strain gauges offer a more consistent measure over time.

I have a CycleOps Fluid2 that's about 11 years old, with roughly 800 hours on it. No leaks, but its silicone-based fluid has broken down to the point where operating viscosity requires a longer and longer warm-up period. I used to track the data when I had my PowerTap wheel, and not only is it measurable, but it's noticeable. About 10 minutes of wheel speed approx. 20 mph and initial temp of 70°F and then there's a dramatic increase in resistance. That's kinda contradictory to the previous statement, but what I mean by noticeable is that day to day, week to week and month to month you won't notice the changes.

I don't plot that trainer any more since getting a Kickr.