DMM Wales have just released this handy step-by-step ‘walk-through’ to aid with the inspection and maintenance of DMM auto-lock carabiner gate mechanisms.
Following on from a visual and tactile assessment, there are three gate action (function) tests described, to ensure that the gate closes fully and reliably. A non-silicone based lubricant such as Duck Oil is recommended to reduce friction at the hinge rivet, within the mechanism and contact areas.
As always, if you have any doubts about the functionality or integrity of a carabiner, take it out of service and seek advice. You can download a PDF of this guide by clicking this link.