I had a similar issue on Sunday. Post wouldn’t come back up, press the lever and pull it it came up, but then waggled about. I tried putting air in it but it was leaking – stick teh end of teh piost in a bucket and it blew bubbles.
I took the post apart and found (mud and water inside…) that the bottom silver end of the top shaft had come slightly unscrewed allowing the o-ring air seal to burb air. I stripped it all, clean it and rebuilt it (with a touch of liquid PTFE and threadlock in appropriate places) and its all lovely and smooth again and working fine.
I guess RS need to loctite the silver end thing in in future.
HTH,
Al