I have a Hohner G3T and the intonation keeps slipping on the treble strings, especially G. When I adjust the saddles they migrate back towards the nut as the screws that hold them still have carved lines into the metal plate and now move within minutes of adjusting while playing.

What can I do to get them to stay in position?
Got it:
Pacifica 604w, Hohner G3T, PRS SE Soapbar I, Schecter Ultra I
Fender 'evil' Twin, Marshall 2554 combo
swap saddles nearest to the locking screw.
Modded Steinberger Spirit (white) (SD-AH/EMG Select)
Modded Steinberger GP-2R (white) (EMG81/60)
Peavey XXL head
Hughes and Kettner Cream Machine
Hughes and Kettner Blues Master