http://finsterwalder-charly.de/en/home/safety-notice-for-click-lock-u-t-lock.html

CL and TL buckles have been developed 30 years ago. Due to the
latest insights on their use in paraglider chest straps, we had to limit their
permissible service life for this kind of application. The reason is that CL and
TL buckles installed in paraglider chest straps are under permanent load and
subject to frequent diagonal load changes. They are, however, not optimally
designed for this kind of stress and the effects of wear out play a role. When a
plug is worn out, the buckle's closure might gradually be pushed open against
the spring pressure of its lock buttons. In the case of heavy wear, the plug can
be pulled out by force. Our later developed P-Lock buckles do not have this
disadvantage.

When the buckles are used in paraglider- and hang glider leg straps, they are
subject to such dynamic loads only during takeoff and landing. However, wear out
after a longer time of use might lead to failure here, too. We therefore limit
the service life also for this application.

Hang glider harness manufacturers have the possibility to rework their
harnesses' CL and TL plugs and therewith extended the buckles' service life from
10 years to a maximum of 20 years in total.