I have a 1978 LP Deluxe with old Grover enclosed, non-locking, non-original tuners. The G string goes out of tune quickly and the tuner does not feel right to the touch. You do 1/4 to 1/2 a turn and nothing happens then, all of a sudden, you make a small turn and the tuning of the string jumps. Also, the screws on the G tuner are often loose and have to be tightened while the other tuner screw remain tight. Is it time for a new set of tuners?
Firstly, if you do replace the tuners then keep the originals! Those Norlin-era Gibsons don't command a lot of money in the used market, and it may be debatable that they never will once the baby boomers move on, but for the time being collectors seem to value originality over any perceived upgrades.
The obvious question, to me at least, is whether the machine head is to blame. G strings seem to have a propensity to bind in the nut slot, and I don't have a lot of faith in Gibson's ability to cut nut slots at the correct depth, width and profile. Have you recently changed string gauge, or even string manufacturer? I would get a guitar tech to make an honest appraisal of the instrument and the tuning issues you are encountering.
Old machine heads can slip, especially if damaged. What you choose to replace them with is a matter of personal preference, but I would try and find something that matches the aesthetics of the original tuner.