In the absence of a dust seal I do wonder how much seal lubricant of any kind will remain under the heat of braking.
It's primarily the resistance to having water ingress Ted, very effective at that.
Unlikely with usage profile on these for the piston to have much heat transferred to it at all.
Comparable though, rear car aluminium calipers that incorporate handbrake mechanism concentric to hydraulic piston, they work perfectly with silicone grease over many years, much compromised with any corrosion effects in them. They even have protective boots, but often seem to succumb to mad jet washing practices.
