As has already been mentioned, the first thing I'd do is replace the recoil and mag springs. Factory springs are fine. (For a while I used Wolff +5% mag springs in a couple of issued 6906's I carried, with factory recoil springs.)
The factory recommendation to armorers for recoil & mag spring replacement used to be based on free length of the springs compared to new ones, but then the company simplified their recommendation by telling armorers to replace recoil & mag springs either every 5 years of use (pretty much meaning mags left fully loaded in LE guns), or every 5,000 rounds fired, whichever came first.
I've seen mags dropped onto hard surfaces (concrete) by cops now and again, and it's not impossible that a "used" mag might have an issue with the lips. New magazines are costly, but a good investment.
Followers can eventually develop a deformation where the lip of the last round digs into the follower under recoil. If that spot gets too rough it might interfere with feeding of the last round, but I've seen them take a lot of abuse and keep feeding normally. I've been reminded by the factory that the black followers used in the 6906 are slightly different than the black ones used in the older 59XX mags (due to the increased slide velocity in the shorter 669/6906 guns and how it can affect feeding). I never could see the subtle differences by eye, but I believed them and kept them separate from those used in the older 59XX mags.
