When the selector drum and forks become worn, renewal is the only practical solution for a reliable gear change mechanism.
Renewal of all the interfacing parts at the same time will provide a smoother more accurate trouble-free gear change.
At the same time check out the gear change lever and linkage for wear of the fulcrums; this can also cause a sloppy change action.
Some of the other components related to this assembly you may wish to replace at the same time: