specialized command post ircc leak

[mtbnoobc]

I put my post in water and can see air coming out from the collar (?) :

https://imgur.com/a/ObtACeq

which part I need to replace?

[droo]

Could be the seal, could be a worn stanchion. The only way you'll find out is to strip the post.

This may sound obvious, but remove the valve core before you start taking anything apart.

[Headshot]

The design is prone to leaks. The seals wear out and if there is external stanchion damage this causes air to escape every time you raise/lower the seat.  They can be serviced with a kit available from Spesh. They may also be able to supply a fresh stanchion. Better bet is to buy a new dropper like a Lyne.

Their last version - 34.9 diameter, which I also own has a different design with the air spring/seal on the inside of the stanchion I believe, so damage to the outside does not cause leaks.