Take it to a local auto parts store and have them test the starter on it. It’s getting cold and that can put added stress on the starter and possibly send it over the edge.
https://youtu.be/d-azByCKQMY
This video should be helpful for you.
One tip is if you’re ever in a pinch and your starter doesn’t work, you can lightly tap it and see if it’ll start but it’s not a guarantee.
Take care, hopefully your son can have his sweet ride back!
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2011 2SS/RS 6M: Hurst Short Throw Equipment, Speed Engineering Headers, Spectre CAI, BTR Stage 3 Camshaft 229/244 .630"/.615" 113+4, Chromoly Pushrods, .660" Springs with steel retainers.