I would try new mags, new recoil spring, and a good cleaning if you haven't already.
Also, make sure your extractor is clean and not broken.
With the age on it you may opt to send it back to Glock for them to go over it. Not sure about now, but years ago they would give it a once over and pretty much a full rebuild for a really good price. Worth looking into.
He who dares wins.
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