I've had one of those 3 piece extending boathooks for years. The inner piece finally bound up in the middle piece, and nothing I could do would free it up. Finally, I sprung for a new one (only $28 at Defender) and decided to find out what was wrong with the old one. Problem was NOT with the twist locks - the design of these locks is pretty bullet proof. Rather, the problem is with some 'clearance' tape used between the sliding sections. My 3 pc pole had two pieces of this tape, one each bonded to the inside of the hook end of the outer and middle sections. One corner of one piece apparently came loose and started to bond itself to the sliding piece. This tore more of it loose until the two pieces were pretty well bonded together.
The adhesive for this tape is relatively mild, and came off the two tubes (ID & OD) with kerosene. This tells me - DO NOT lubricate these boat hooks with anything but fresh water. Keeping the tubes clean and smooth is also good.
The old boat hook has been reassembled, admittedly a few inches shorter than it used to be. The only way to remove the fittings from the tubes is with a hacksaw. Then you can split the tube end, remove it from the fitting, then reinstall the fitting - easy with a hammer and a nail set. Handle was glued on and had to be split for removal. Handle has been reinstalled with friction tape, which will soon get a layer of cockscombing (& perhaps a couple of turks heads). Or maybe I'll just leave it with the friction tape - looks rude and crude.