The only thing plastic about it is the nut (button). The mag catch body is steel. (If you ever have one outside the frame, you can use a magnet to pick it up.)
The nut is a 1-time installation/use item that snaps on (and off) the left end of the mag catch body (a raised ring/rib inside the nut). If it's removed it should be replaced with a new one.
This picture shows the Value Line (and CS series) mag catch & nut on the top, and the standard mag body & threaded nut on the bottom.
There's also a "tornado" spring located under the plastic nut, around the shaft of the mag catch body and with the large end against the back of the nut. (Not shown in the above picture.)
As an armorer, I'd leave it alone unless it has to be replaced due to an actual problem.