It can never be fixed. I heard it from a guy at the gun shop who was wearing black BDUs and a tactical fanny pack, so he must know. Judging from the responses above, including changing the wrong parts, etc., he's probably right.
You should quit shooting Glocks.
The person who has nothing for which he is willing to fight, nothing … more important than his own personal safety, is a miserable creature [with] no chance of being free unless made and kept so by the exertions of better men …. John Stuart Mill