In praise of the old leather seal

[eyebull]

I converted my Webley Vulcan to a leather seal over thirty years ago; it's still on the same one, and is smooth and very consistent. My Ospreys are similarly converted.
As Hsing-ee says, leather is very tolerant of cylinder wall irregularity, but they need to be sized to a good fit. Usually a relatively loose fit works best, it should be very easy to push it down the cylinder. Too tight will rob it of power.

This is intriguing. I'd be curious to know if other modern springers could be converted to leather, and how it would affect their real-world performance.