I have found when you mix non gulp plastics with gulp in the sauce, everything gets ruined over time. Gulp baits become stiffer, and other baits deteriorate, change colour etc etc . Otherwise, that brine lasts a long time so long as it isn't tainted by other non gulp baits.
And, make sure your gulps are always submerged, ie the brine should pretty much be to the top of your container !!!