Graphite for bridge and nut slots helps a lot to prevent binding and then slipping which results in being out of tune as already mentioned. Meticulous winding when installing is vital. Slapping them on and then willy-nilly winding results in slippage and tuning issues every time. It could be as bad as having a faulty tuner with bad gearing maybe or just worn out, it happens. Les Paul style guitars are notorious for the G string going out, something about the design and angle of the string? I can't remember now. If you don't know how to do it, having a professional setup of your guitars can produce amazing results. I have all the tools and measuring devices etc. and it is not hard to learn but is a skill that guitarists need, or at least need to pay for! You find a good Luthier and have them inspect all the guitars. There could be issues that you don't know about causing the problem, some if not most are easily remedied by a professional. Do some research if you go the Luthier route. There are good and bad ones just like anything else.

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