In spite of my opinion of the OEM design, to reinstall it you have to remove the cap that holds the spring in it, to take the spring tension off the plunger while you reinstall it. Otherwise the plunger will keep plunging back when you try to stick the tensioner back in. You put the spring and cap back after installing, then the plunger will advance to take up tension...

And if you are lucky it will keep the adjustment proper. If not you should replace it with a manual unit. If you see that wear pattern on the teeth or a polished strip on the back of the rack you need to go to the manual unit.

The problem happens when the tensioner can not adjust far enough to seat properly.

Anyone here who has used a manual tensioner will tell you they're easy to live with, seldom requiring adjustment.