On 19 Sep, 10:28, Adrian Simpson wrote:

Any suggestions ?

Probably your gas strut is now merely a strut, having lost its gas.

#1 New chair. These things aren't fixable, aren't intended to be
fixable.

#2 New gas strut. Unless you're buying containerloads from China, new
struts from strut shops cost more than a new chair from Viking.

#3 Another gas strut from another chair. Good fix in offices, as
there's usually a gradual attrition of chairs for different reasons
and you cna find spares.

#4 Convert it to a mechanically clamped chair, rather than a bouncy
strut. If it's your chair, and your chair alone, this isn't a bad
thing.