Witter detachable tow bars

Posted this once already but maybe I did not press the right buttons. Not clear to me but here goes again and hopefully with picture. 
have had this detachable tow bar for around 5 years or so and no problems apart from the strength needed to turn the blue bar to make the ball arm ready for locating in the socket and also for removing.

but now unable to remove the arm which has been on for only 5 days, normally being in the habit of removing when not in use to avoid extra damage if get shunted in the rear, which I have not had in over 40 years.

talked to patient guy at Witter who said squirting with lubricant should solve problem. It has not.

The blue release bar turns when depressed and turned clockwise but no click and no release. Also the resistance to turning clockwise seems different and less resistance compared to before. Also possible to turn the blue bar more than the 90 degrees normally done clockwise to release.

any suggestions gratefully received. Have noted a comment on u tube that the blue release bar can get gunge which inhibits its operation. Am wondering if the blue bar not engaging with the release mechanism on the arm

thanks for any helpful ideas