There's holes in the damper plunger, I think that's what it's called, and it also has a lockout on which you can see when it's apart how it works, just covers two holes up. Changed the oil, put the top back on the damper and then screw the hole thing back into the uppers. Then slide the lowers on and bolt it up at the bottom and put the rebound adjuster back in. So yeah you could say it is sealed, but it can be taken apart for oil changes and new seals. It felt better on the damping last night just messing about on a local trail so I'll see what happens. Worst situation is I can just put 10wt back in. It's only a 20min job to sort it out