Mineral oil works well to soften and juice them up when they get dry and sticky.
I believe this is what the factory uses to package new soft rubber baits in for retail.
Just a warning though, be careful some types of fish attractants (the old baitmate brand for exp.) will make your baits get stiff or melt.
Barlow's sells some flavored oils that are safe if you want grape, watermelon, strawberry etc. .
..The Original old style Side imaging sonar..
With 360* degree side scanning.