KS e30 seatpost cartridge change

Hello !

A problematic post, these sealed cartridges inside seat posts look to be replacable, I wondered if anyone had managed to swap one out before ?  Lots of guides about, however this one seems not to have a fixing at the seat end of the seat post anchor to unscrew the cartridge. Currently the stainless rod and larger diameter outer casing of the cartrige spin freely in relation to the black seat post. Does anyone know how to disassemble this model ? The knee joints would be very grateful!