Dropper post wont stop dropping

I have a KS eTen R dropper post on my MTB. It had been working properly for the last two seasons but now when I sit on it the post slowly drops all the way down to the lowered position. When I stand up or get off the bike the post slowly goes back up. This happens even if I disconnect the remote cable - so I don't think its a cable tension/adjustment issue (but I'm willing to be wrong)

Not sure whether to try and service this or if its just time for a new one.